Solid State Light Fixtures Suitable for High Temperature Operation Having Separate Blue-Shifted-Yellow/Green and Blue-Shifted-Red Emitters

ABSTRACT

Solid state light fixtures include a plurality of blue-shifted-yellow/green light emitting diode (“LED”) packages and a plurality of blue-shifted-red LED packages, where the solid state light fixture emits light having a correlated color temperature of between 1800 K and 5500 K, a CRI value of between 80 and 99, a CRI R9 value of between 15 and 75, and a Qg value of between 90 and 110 when the blue-shifted-yellow/green LED packages and the blue-shifted-red LED packages are operating at steady-state operating temperatures of at least 80° C.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to U.S.Provisional Patent Application Ser. No. 62/262,414, filed Dec. 3, 2015,the entire content of which is incorporated herein by reference as ifset forth in its entirety.

BACKGROUND

The present invention relates to solid state light fixtures and, moreparticularly, to solid state light fixtures that are suitable for hightemperature operation that emit white light at high luminous efficiencywhile maintaining good color rendering properties.

A wide variety of light emitting devices are known in the art including,for example, incandescent light bulbs, fluorescent light bulbs andso-called “solid state” lighting devices that use light emitting diodes(“LEDs”) as the light source. LEDs generally include a series ofsemiconductor layers that may be epitaxially grown on a substrate. Oneor more semiconductor p-n junctions are formed in these epitaxiallayers. When a sufficient voltage is applied across the p-n junction,electrons in the n-type semiconductor layers and holes in the p-typesemiconductor layers flow toward the p-n junction. As the electrons andholes flow toward each other, some of the electrons will “collide” withcorresponding holes and recombine. Each time this occurs, a photon oflight is emitted, which is how LEDs generate light. The wavelengthdistribution of the light generated by an LED generally depends on thesemiconductor materials used and the structure of the thin epitaxiallayers that make up the “active region” of the device (i.e., the areawhere the electrons and holes recombine).

Most LEDs are nearly monochromatic light sources that appear to emitlight having a single color. Thus, the spectral power distribution ofthe light emitted by most LEDs is tightly centered about a “peak”wavelength, which is the single wavelength where the spectral powerdistribution or “emission spectrum” of the LED reaches its maximum asdetected by a photo-detector. The “width” of the spectral powerdistribution of most LEDs is between about 10 nm and 30 nm, where thewidth is measured at half the maximum illumination on each side of theemission spectrum (this width is referred to as thefull-width-half-maximum or “FWHM” width).

In order to use LEDs to generate white light, LED-based light emittingdevices have been provided that include several LEDs that each emit alight of a different color. The different colored light emitted by theLEDs combine to produce white light. For example, by simultaneouslyenergizing red, green and blue LEDs, the resulting combined light mayappear white, or nearly white, depending on, for example, the relativeintensities, peak wavelengths and spectral power distributions of thesource red, green and blue LEDs.

White light may also be produced by surrounding a single blue LED withone or more phosphors that convert some of the light emitted by the LEDto light of one or more other colors. The combination of the lightemitted by the single-color LED that is not converted by the phosphorsand the light of other colors that is emitted by the phosphors mayproduce a white or near-white light.

As one example, a white light emitting LED package may be formed bycoating a gallium nitride-based blue LED (i.e., an LED that emits lighthaving a peak wavelength in the blue color range as defined herein) witha “yellow” phosphor (i.e., a phosphor that emits light having a peakwavelength in the yellow color range) such as a cerium-doped yttriumaluminum garnet phosphor, which has the chemical formula Y₃Al₅O₁₂:Ce,and is commonly referred to as YAG:Ce. The blue LED emits light having apeak wavelength of, for example, about 460 nm. Some of blue lightemitted by the LED passes between and/or through the YAG:Ce phosphorparticles without being converted, while other of the blue light emittedby the LED is absorbed by the YAG:Ce phosphor, which becomes excited andemits yellow fluorescence with a peak wavelength of about 550 nm (i.e.,the blue light is converted to yellow light). The combination of bluelight and yellow light that is emitted by the LED package may appearwhite to an observer. Such light is typically perceived as being coolwhite in color, as it is primarily comprises light on the lower half(shorter wavelength side) of the visible emission spectrum. To make theemitted white light appear more “warm” and/or exhibit better colorrendering properties, red phosphors such as Eu²⁺ doped CaAlSiN₃ basedphosphor particles may be added to the coating applied to the blue LED.

In general, phosphors absorb light having first wavelengths and re-emitlight having second wavelengths that are different (typically longer)than the first wavelengths. For example, “down-conversion” phosphors mayabsorb light having shorter wavelengths and re-emit light having longerwavelengths. It will be understood that the term “phosphor” is usedbroadly herein to encompass not only materials that have traditionallybeen referred to as phosphorescent, but also other luminophoricmaterials such as, for example, quantum dots, that absorb light at onewavelength and re-emit light at a different wavelength in the visiblespectrum.

Typically, particles of a phosphor are mixed into a binder material suchas, for example, an epoxy-based or silicone-based curable resin, and arethen coated, sprayed or poured onto an LED or another surface of a lightfixture. Herein, such mixtures are referred to as a “recipientluminophoric medium.” A recipient luminophoric medium may include onelayer or the like in which one or more phosphors are mixed, multiplestacked layers, each of which may include one or more of the same ordifferent phosphors, and/or multiple spaced apart layers, each of whichmay include the same or different phosphors.

SUMMARY

Pursuant to embodiments of the present invention, solid state lightfixtures are provided that include a plurality ofblue-shifted-yellow/green LED packages and a plurality ofblue-shifted-red LED packages. These solid state light fixtures emitlight having a correlated color temperature of between 1800 K and 5500K, a CRI value of between 80 and 99, a CRI R9 value of between 15 and75, and a Qg value of between 90 and 110 when theblue-shifted-yellow/green LED packages and the blue-shifted-red LEDpackages are operating at steady-state operating temperatures of atleast 80° C.

In some embodiments, each blue-shifted-yellow/green LED package maycomprise a first blue LED and an associated first recipient luminophoricmedium that includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and each blue-shifted-red LED package may comprise a secondblue LED and an associated second recipient luminophoric medium thatincludes a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In suchembodiments, the first blue LEDs may have a first average peakwavelength that is less than a second average peak wavelength of thesecond blue LEDs. At least one of the first blue LEDs may have a peakwavelength that is less than 455 nm and at least one of the second blueLEDs may have a peak wavelength that is more than 460 nm. In someembodiments, the plurality of blue-shifted-red LED packages may comprisea first plurality of blue-shifted-red LED packages, and the solid statelight fixture may further include a second plurality of blue-shifted-redLED packages, each of which comprises a third blue LED and an associatedthird recipient luminophoric medium that includes a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelength that isgreater (i.e., a higher wavelength) than a peak wavelength of the first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

In some embodiments, the second recipient luminophoric mediums that areassociated with each of the second blue LEDs may further include asecond (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelengththat is greater than a peak wavelength of the first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. Additionally, at least some of thefirst recipient luminophoric mediums may include both the Y₃Al₅O₁₂:Cephosphor and the Lu₃Al₅O₁₂:Ce phosphor. The solid state light fixturemay be, for example, an A19 or A21 light bulb, and the first and secondblue LEDs may be surface mounted on a printed circuit board or othersubmount such that each of the first blue LEDs is immediately adjacent arespective one of the second blue LEDs.

In some embodiments, the second recipient luminophoric mediums may notinclude either a yellow phosphor or a green phosphor, and the firstrecipient luminophoric mediums may not include a red phosphor. The first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a peak wavelength between615 and 624 nm and the second (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor mayhave a peak wavelength between 625 nm and 640 nm. Additionally, in someembodiments, a first of the blue-shifted-yellow/green LED packages and afirst of the blue-shifted-red LED packages may be implemented togetheras a packaged LED component that includes at least one LED on a submountand a first recipient luminophoric medium that only includes yellowand/or green phosphors on a first side of the submount and a secondrecipient luminophoric medium that only includes red phosphors on asecond side of the submount that is opposite the first side.

Pursuant to further embodiments of the present invention, packaged LEDcomponents are provided that include a submount having an LED mountingsurface; at least one LED on the LED mounting surface; and a firstrecipient luminophoric medium having a first phosphor on top of a firstregion of the LED mounting surface and a second recipient luminophoricmedium having a second phosphor that is different from the firstphosphor and that emits light having a peak wavelength in the red colorrange on top of the second region of the LED mounting surface. The firstrecipient luminophoric medium is separate from the second recipientluminophoric medium and the second recipient luminophoric medium is noton top of the first region and the first recipient luminophoric mediumis not on top of the second region. The combination of the light emittedby the at least one LED and the first recipient luminophoric medium isnot white light.

In some embodiments, the packaged LED component may further include adivider that extends across the LED mounting surface to define the firstregion and the second region. The LED mounting surface may be within acavity, and the divider may divide the cavity into first and secondsub-cavities, and the first recipient luminophoric medium may be in thefirst sub-cavity and the second recipient luminophoric medium may be inthe second sub-cavity. The submount may include a molded structure thatdefines the cavity and the first and second sub-cavities. The firstrecipient luminophoric medium may include a Y₃Al₅O₁₂:Ce phosphor and/ora Lu₃Al₅O₁₂:Ce phosphor and may emit light having a peak wavelength inthe green or yellow color range, and the second recipient luminophoricmedium may include at least a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor. The distance between the first sub-cavity and the secondsub-cavity may be less than two centimeters.

The at least one LED may comprise a first LED within the firstsub-cavity and a second LED within the second sub-cavity. The dividermay comprise a separate structure from the material that defines thecavity. The divider may be formed of, for example, a reflective plasticmaterial. The first and second LEDs may have different peak wavelengths.

Pursuant to further embodiments of the present invention, solid statelight fixtures are provided that comprise a plurality ofblue-shifted-yellow/green LED packages and a plurality ofblue-shifted-red LED packages, where the light emitted by the solidstate light fixture has an emission spectrum having a first peak in theblue color range, a second peak between 525 nm and 575 nm, and a thirdpeak between 610 nm and 650 nm, and where the third peak is larger thanboth the first peak and the second peak.

In some embodiments, each blue-shifted-yellow/green LED package maycomprise a first blue LED and an associated first recipient luminophoricmedium that includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and each blue-shifted-red LED package may comprise a secondblue LED and an associated second recipient luminophoric medium thatincludes a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In otherembodiments, each blue-shifted-yellow/green LED package may comprise afirst blue LED and an associated first recipient luminophoric mediumthat includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor, andeach blue-shifted-red LED package may comprise a second blue LED and anassociated second recipient luminophoric medium that includes a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor and a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that emits light having a peakwavelength that is higher than the peak wavelength of the light emittedby the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

In some embodiments, the solid state light fixture may emit light havinga correlated color temperature of between 1800 K and 5500 K, a CRI valuebetween 80 and 99, a CRI R9 between 15 and 75, and a Qg value between 90and 110 when the blue-shifted-yellow/green LED packages and theblue-shifted-red LED packages are operating at steady-state operatingtemperatures of at least 80° C.

In some embodiments, the blue LEDs included in theblue-shifted-yellow/green LED packages may have a first average peakwavelength that is less than a second average peak wavelength of theblue LEDs included in the blue-shifted-red LED packages. The pluralityof blue-shifted-red LED packages may comprise a first plurality ofblue-shifted LED packages, and the solid state light fixture may furtherinclude a second plurality of blue-shifted-red LED packages, each of thesecond plurality of blue-shifted-red LED packages comprising a thirdblue LED and an associated third recipient luminophoric medium thatincludes a second (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peakwavelength that is greater than a peak wavelength of the first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

In some embodiments, at least some of the first recipient luminophoricmediums may include both the Y₃Al₅O₁₂:Ce phosphor and/or theLu₃Al₅O₁₂:Ce phosphor. The second recipient luminophoric mediums may notinclude either a yellow phosphor or a green phosphor, and the firstrecipient luminophoric mediums may not include a red phosphor.

In some embodiments, the second peak may be a shoulder formed on a sideof the third peak. In such embodiments, the second peak may be between535 nm and 555 nm, and the third peak may be between 615 nm and 630 nm.

Pursuant to still further embodiments of the present invention, lightingapparatus includes a three dimensional shaped optically transmissiveenclosure having an interior volume; a plurality of distinctyellow/green light emitting regions that are within the interior volume,the yellow/green light emitting regions comprising at least one galliumnitride based LED that produces shorter wavelength light and at leastone first recipient luminophoric medium that downconverts at least someof the shorter wavelength light to longer wavelength light; and aplurality of distinct red/orange light emitting regions that are withinthe interior volume, the red/orange light emitting regions comprising atleast one gallium nitride based LED that produces shorter wavelengthlight and at least one second recipient luminophoric medium thatdownconverts at least some of the shorter wavelength light to longerwavelength light. The lighting apparatus emits white light from theoptically transmissive enclosure having a correlated color temperaturebetween 1800 K and 5500 K and a CRI value of greater than 80.

In some embodiments, the at least one first recipient luminophoricmedium may include a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and the at least one second recipient luminophoric medium mayinclude a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. The at least onesecond recipient luminophoric medium may include a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelength that isgreater than a peak wavelength of the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor.

In some embodiments, the lighting apparatus may further include a secondplurality of distinct red/orange light emitting regions that are withinthe interior volume, the second red/orange light emitting regionscomprising at least one gallium nitride based LED that produces shorterwavelength light and at least one third recipient luminophoric mediumthat downconverts at least some of the shorter wavelength light tolonger wavelength light, where a peak wavelength of the light emitted bythe at least one third recipient luminophoric medium exceeds a peakwavelength of the light emitted by the at least one second recipientluminophoric medium.

In some embodiment, the lighting apparatus may emit light having acorrelated color temperature of between 1800 K and 5500 K, a CRI valuebetween 80 and 99, a CRI R9 value between 15 and 75, and a Qg valuebetween 90 and 110 when the gallium nitride based LEDs are operating atsteady-state operating temperatures of at least 80° C. The at least onegallium nitride based LED included in the distinct yellow/green lightemitting regions may have a peak wavelength that is less than 455 nm andthe at least one gallium nitride based LED included in the distinctred/orange light emitting regions may have a peak wavelength that ismore than 460 nm. The at least one first recipient luminophoric mediummay include both a Y₃Al₅O₁₂:Ce phosphor and a Lu₃Al₅O₁₂:Ce phosphor. Thelighting apparatus may comprise an A series light bulb.

Pursuant to yet additional embodiments of the present invention, alighting apparatus is provided that includes an optically transmissiveenclosure comprising an interior volume and shaped in accordance with anA series bulb; a plurality of distinct yellow/green light emittingregions that are configured to emit light into the interior volume, theyellow/green light emitting regions comprising at least one galliumnitride based LED that produces shorter wavelength light and at leastone first recipient luminophoric medium that downconverts at least someof the shorter wavelength light to longer wavelength light; and aplurality of distinct red/orange light emitting regions that areconfigured to emit light into the interior volume, the red/orange lightemitting regions comprising at least one gallium nitride based LED thatproduces shorter wavelength light and at least one second recipientluminophoric medium that downconverts at least some of the shorterwavelength light to longer wavelength light.

In some embodiments, the at least one first recipient luminophoricmedium may include a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and the at least one second recipient luminophoric medium mayinclude a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. For example, theat least one second recipient luminophoric medium may include a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelength that isgreater than a peak wavelength of the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor.

In some embodiments, the lighting apparatus may further include a secondplurality of distinct red/orange light emitting regions that areconfigured to emit light into the interior volume, the second red/orangelight emitting regions comprising at least one gallium nitride based LEDthat produces shorter wavelength light and at least one third recipientluminophoric medium that downconverts at least some of the shorterwavelength light to longer wavelength light, wherein a peak wavelengthof the light emitted by the at least one third recipient luminophoricmedium exceeds a peak wavelength of the light emitted by the at leastone second recipient luminophoric medium.

The lighting apparatus may emit light having a correlated colortemperature of between 1800 K and 5500 K, a CRI value between 80 and 99,a CRI R9 value between 15 and 75, and a Qg value between 90 and 110 whenthe gallium nitride based LEDs are operating at steady-state operatingtemperatures of at least 80° C.

The at least one gallium nitride based LED included in the distinctyellow/green light emitting regions may have a peak wavelength that isless than 455 nm and the at least one gallium nitride based LED includedin the distinct red/orange light emitting regions may have a peakwavelength that is more than 460 nm. The at least one first recipientluminophoric medium may include both a Y₃Al₅O₁₂:Ce phosphor and aLu₃Al₅O₁₂:Ce phosphor.

Pursuant to yet additional embodiments of the present invention,A-series solid state light bulbs are provided that comprise an A-serieslight bulb body; a diffuse optical enclosure mounted on the A-serieslight bulb body; a reflector within the diffuse optical enclosure; and asubmount having at least one blue-shifted-yellow/green emitter and atleast one blue-shifted-red emitter in a central section of the submountand a plurality of blue-shifted-yellow/green emitters and a plurality ofblue-shifted-red emitters arranged around a periphery of the submount.Each blue-shifted-yellow/green emitter emits light having a peakwavelength in the yellow or green color ranges and each blue-shifted-redemitter emits light having a peak wavelength in the red color range.

In some embodiments, the at least one blue-shifted-yellow/green emitterand the at least one blue-shifted-red emitter in the central section ofthe submount may comprise a packaged LED component that includes atleast one blue LED on an LED mounting surface, a first recipientluminophoric medium having a first phosphor on top of a first region ofthe LED mounting surface and a second recipient luminophoric mediumhaving a second phosphor that is different from the first phosphor ontop of a second region of the LED mounting surface, where the firstrecipient luminophoric medium is separate from the second recipientluminophoric medium and the second recipient luminophoric medium is noton top of the first region and the first recipient luminophoric mediumis not on top of the second region.

In some embodiments, the first and second recipient luminophoric regionsmay be disposed side-by-side on the at least one LED. The plurality ofblue-shifted-yellow/green emitters and the plurality of blue-shifted-redemitters that are arranged around the periphery of the submount maycomprise a plurality of packaged LED components, each packaged LEDcomponent including at least one blue LED on a respective LED mountingsurface, a first recipient luminophoric medium having a first phosphoron top of a first region of the LED mounting surface and a secondrecipient luminophoric medium having a second phosphor that is differentfrom the first phosphor on top of a second region of the LED mountingsurface, where the first recipient luminophoric medium is separate fromthe second recipient luminophoric medium and the second recipientluminophoric medium is not on top of the first region and the firstrecipient luminophoric medium is not on top of the second region.

The reflector may be positioned above the submount and may have atruncated frusto-conical shape.

Pursuant to additional embodiments of the present invention, solid statelight fixtures are provided that comprise a diffuse optical enclosurehaving an interior volume; a plurality of blue-shifted-yellow/greenemitters that are configured to emit light into the interior volume; aplurality of blue-shifted-red emitters that are configured to emit lightinto the interior volume; and a controller that controls the relativecurrent levels provided to the plurality of blue-shifted-yellow/greenemitters and the plurality of blue-shifted-red emitters. The controlleris configured to increase the relative amount of drive current suppliedto the blue-shifted-red emitters as compared to theblue-shifted-yellow/green emitters when the solid state light fixture isdimmed. The solid state light fixture may be an A-19 or A-21 solid statelight bulb.

In some embodiments, the correlated color temperature of the lightemitted from the diffuse optical enclosure may generally decrease withan increasing level of dimming.

In some embodiments, each blue-shifted-yellow/green emitter may be afirst blue LED and an associated first recipient luminophoric mediumthat includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor, andeach blue-shifted-red emitter may be a second blue LED and an associatedsecond recipient luminophoric medium that includes a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In other embodiments, eachblue-shifted-yellow/green emitter may be a first blue LED and anassociated first recipient luminophoric medium that includes aY₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor, and some of theblue-shifted-red emitters may each comprise a second blue LED and anassociated second recipient luminophoric medium that includes a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor and others of the blue-shifted-redemitters may each comprise a third blue LED and an associated thirdrecipient luminophoric medium that includes a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelength that isgreater than a peak wavelength of the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor.

Each blue-shifted-yellow/green emitter may comprise a first blue LED andan associated first recipient luminophoric medium that includes aY₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor, and eachblue-shifted-red emitter may comprise a second blue LED and anassociated second recipient luminophoric medium that includes a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor and a second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelength that isgreater than a peak wavelength of the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor.

Pursuant to still further embodiments of the present invention, solidstate light fixtures are provided that include a body; a diffuse opticalenclosure mounted on the body; a reflector and/or a secondary opticalstructure within the diffuse optical enclosure; and a submount having atleast one blue-shifted-yellow/green emitter and at least oneblue-shifted-red emitter in a central section of the submount and aplurality of blue-shifted-yellow/green emitters and a plurality ofblue-shifted-red emitters arranged around a periphery of the submount.Each blue-shifted-yellow/green emitter emits light having a peakwavelength in the yellow or green color ranges and each blue-shifted-redemitter emits light having a peak wavelength in the red color range.

In some embodiments, the at least one blue-shifted-yellow/green emitterand at least one blue-shifted-red emitter in the central section of thesubmount may comprise a packaged LED component that includes at leastone blue LED on an LED mounting surface, a first recipient luminophoricmedium having a first phosphor on top of a first region of the LEDmounting surface and a second recipient luminophoric medium having asecond phosphor that is different from the first phosphor on top of asecond region of the LED mounting surface, where the first recipientluminophoric medium is separate from the second recipient luminophoricmedium and the second recipient luminophoric medium is not on top of thefirst region and the first recipient luminophoric medium is not on topof the second region.

In some embodiments, the first and second recipient luminophoric regionsmay be disposed side-by-side on the at least one blue LED. The pluralityof blue-shifted-yellow/green emitters and the plurality ofblue-shifted-red emitters that are arranged around the periphery of thesubmount may comprise a plurality of packaged LED components, eachpackaged LED component including at least one blue LED on a respectiveLED mounting surface, a first recipient luminophoric medium having afirst phosphor on top of a first region of the LED mounting surface anda second recipient luminophoric medium having a second phosphor that isdifferent from the first phosphor on top of a second region of the LEDmounting surface, where the first recipient luminophoric medium isseparate from the second recipient luminophoric medium and the secondrecipient luminophoric medium is not on top of the first region and thefirst recipient luminophoric medium is not on top of the second region.

The secondary optical structure may comprise a total internal reflectoroptic that reflects a first portion of the light from the at least oneblue-shifted-yellow/green emitter, the at least one blue-shifted-redemitter, the plurality of blue-shifted-yellow/green emitters and/or theplurality of blue-shifted-red emitters and that receives andsubstantially totally internally reflects a second portion of the lightfrom the at least one blue-shifted-yellow/green emitter, the at leastone blue-shifted-red emitter, the plurality of blue-shifted-yellow/greenemitters and/or the plurality of blue-shifted-red emitters.

Pursuant to yet additional embodiments of the present invention, LEDbased light fixtures are provide that include a plurality ofblue-shifted-yellow/green LED packages, the blue-shifted-yellow/greenLED packages including low-phosphor LED packages and high phosphor LEDpackages, the high phosphor LED packages having a higher phosphorconversion ratio than the low phosphor LED packages; and a plurality ofblue-shifted-red LED packages. The blue-shifted-red LED packages extendin a first row, and a first subset of the blue-shifted-yellow/green LEDpackages extend in a second row on a first side of the blue-shifted-redLED packages and a second subset of the blue-shifted-yellow/green LEDpackages extend in a third row on a second side of the blue-shifted-redLED packages that is opposite the first side.

In some embodiments, the blue-shifted-yellow/green LED packages in thesecond row may include both low phosphor LED packages and high phosphorLED packages. The blue-shifted-yellow/green LED packages in the thirdrow may also include both low phosphor LED packages and high phosphorLED packages. The blue-shifted-red LED packages may be electricallyconnected in series to form a first LED string and the low phosphor LEDpackages may be electrically connected in series to form a second LEDstring. The second LED string may cross the first LED string in at leastfour locations. Likewise, the high phosphor LED packages may beelectrically connected in series to form a third LED string, and thisthird LED string may cross the first LED string in at least fourlocations. The third LED string may also cross the second LED string inat least four locations. The light fixture may include additionalstrings of blue-shifted-yellow/green LED packages and/or ofblue-shifted-red LED packages.

In some embodiments, a first end of the second row may extend beyond afirst end of the first row, and a second end of the second row mayextend beyond a second end of the first row. Similarly, a first end ofthe third row may extend beyond the first end of the first row, and asecond end of the third row may extend beyond the second end of thefirst row.

In some embodiments, the high phosphor LED packages may each include afirst amount of a first phosphor and the low phosphor LED packages mayeach include a second amount of the first phosphor, where the firstamount is between twice and seven times the second amount. In otherembodiments, the first amount may be between three times and six timesthe second amount.

In some embodiments, an average separation between adjacent ones of theblue-shifted-red LED packages in the first row may be less than anaverage separation between adjacent ones of theblue-shifted-yellow/green LED packages in the second row. Similarly, anaverage separation between adjacent ones of the blue-shifted-red LEDpackages in the first row may be less than an average separation betweenadjacent ones of the blue-shifted-yellow/green LED packages in the thirdrow.

Pursuant to further embodiments of the present invention, tunableLED-based light fixtures are provided that include a plurality ofblue-shifted-yellow/green LED packages, the blue-shifted-yellow/greenLED packages including low-phosphor LED packages that each include afirst amount of a first phosphor and high phosphor LED packages thateach include a second amount of the first phosphor and a plurality ofblue-shifted-red LED packages, where the second amount is between twoand seven times the first amount.

In some embodiments, the blue-shifted-red LED packages may extend in afirst row and the blue-shifted-yellow/green LED packages may extend in asecond row and in a third row, with the second row extending on a firstside of the first row and the third row extending on a second side ofthe first row that is opposite the first side. The second and third rowsmay be generally parallel to the first row. The second row may includeboth low phosphor LED packages and high phosphor LED packages, and thethird row may include both low phosphor LED packages and high phosphorLED packages.

In some embodiments, the blue-shifted-red LED packages may beelectrically connected in series to form a first LED string and the lowphosphor LED packages may be electrically connected in series to form asecond LED string. The second LED string may cross the first LED stringin at least four locations. Likewise, the high phosphor LED packages maybe electrically connected in series to form a third LED string, and thisthird LED string may cross the first LED string in at least fourlocations. In some embodiments, the third LED string may cross thesecond LED string in at least four locations.

In some embodiments, a second line defined by the second row may haverespective endpoints that extend beyond respective endpoints of a firstline defined by the first row, and/or a third line defined by the thirdrow may have respective endpoints that extend beyond respectiveendpoints of the first line. In some embodiments, an average separationbetween adjacent ones of the blue-shifted-red LED packages in the firstrow may be less than an average separation between adjacent ones of theblue-shifted-yellow/green LED packages in the second row, and/or theaverage separation between adjacent ones of the blue-shifted-red LEDpackages in the first row may be less than an average separation betweenadjacent ones of the blue-shifted-yellow/green LED packages in the thirdrow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a 1931 CIE Chromaticity Diagram illustrating thelocation of the planckian locus.

FIG. 2 is a graph illustrating the reflectance spectra for the CRI R1-R9color samples when illuminated by a reference light source.

FIG. 3 is a graph illustrating the response of the human eye to light inthe visible light spectrum.

FIG. 4 is a graph illustrating the emission spectra as a function ofoperating temperature for a “true white” solid state light fixture thatincludes blue-shifted yellow LED packages and red AlInGaP LEDs.

FIG. 5A is a graph illustrating the relative luminous flux as a functionof operating temperature output by a blue-shifted-red LED package and ared AlInGaP LED.

FIG. 5B is a graph illustrating the change in peak wavelength as afunction of operating temperature for both a blue-shifted-red LEDpackage and a red AlInGaP LED.

FIG. 6 is a graph illustrating the absorption spectrum for fourrepresentative red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors.

FIG. 7 is a graph illustrating the intensity of the radiation emitted asa function of wavelength of a conventional phosphor-converted white LEDpackage that uses a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

FIG. 8 is a graph illustrating the intensities of the radiation emittedas a function of wavelength for the blue-shifted-yellow LED packages andthe blue-shifted-red LED packages that are included in a solid statelight fixture according to embodiments of the present invention.

FIG. 9 is a graph illustrating the intensity of the radiation emitted asa function of wavelength for a solid state light fixture according toembodiments of the present invention.

FIG. 10 is a graph comparing the emission spectrum of a solid statelight fixture that has a conventional phosphor-converted white LED thatuses a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor to the emission spectrum ofa solid state light fixture according to embodiments of the presentinvention.

FIG. 11A is a schematic perspective view of a solid state light bulbaccording to embodiments of the present invention with the dome omitted.

FIG. 11B is a perspective view of a printed circuit board that isincluded in the solid state light bulb of FIG. 11A that has sevenblue-shifted-yellow LED packages and seven blue-shifted-red LED packagesmounted thereon.

FIG. 11C is a cross-sectional view of the solid state light bulb of FIG.11A with a reflector omitted to better show the printed circuit board.

FIG. 11D is a perspective view of an alternative reflector that may beused in the solid state light bulb of FIGS. 11A-11C in other embodimentsof the present invention.

FIG. 11E is a cross-sectional view of a solid state light bulb accordingto further embodiments of the present invention.

FIG. 12A is a plan view of a surface-mounted LED package that includestwo LEDs mounted in separate sub-cavities.

FIG. 12B is a plan view of the surface-mounted LED package of FIG. 12Awith two different types of recipient luminophoric mediums depositedinto the respective sub-cavities.

FIG. 13 is a schematic side view of an LED package according to furtherembodiments of the present invention.

FIG. 14 is a schematic side view of an LED package according to stillfurther embodiments of the present invention.

FIG. 15A illustrates a PAR-series downlight according to furtherembodiments of the present invention.

FIG. 15B illustrates a troffer light fixture according to furtherembodiments of the present invention.

FIG. 15C illustrates a solid state streetlight according to stillfurther embodiments of the present invention.

FIG. 15D illustrates a solid state downlight according to still furtherembodiments of the present invention.

FIGS. 16A-16D illustrate a solid state light bulb according to stillfurther embodiments of the present invention.

FIG. 17A is a perspective view of a troffer light fixture according tofurther embodiments of the present invention.

FIG. 17B is a plan view of the troffer light fixture of FIG. 17A.

FIG. 17C is a perspective view of the LED package mounting surface andLED packages included in the troffer light fixture of FIG. 17A.

FIG. 17D is a graph that illustrates the emission spectra of aconventional troffer light fixture and the troffer light fixture ofFIGS. 17A-17C.

FIG. 18A is a perspective view of a tunable troffer light fixtureaccording to further embodiments of the present invention.

FIG. 18B is an enlarged view of a portion of the LED package mountingsurface and LED packages of the tunable troffer light fixture of FIG.18A.

FIG. 18C is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating a range of color points that may be achieved using thetunable troffer light fixture of FIG. 18A.

FIG. 18D is a graph illustrating the intensity of the radiation emittedas a function of wavelength for each of the different types of LEDpackages included in the tunable troffer light fixture of FIG. 18A.

FIG. 18E is a graph illustrating the intensity of the radiation emittedas a function of wavelength for the tunable troffer light fixture ofFIG. 18A when operated to fall within the E3 through E7 regions of FIG.18C by controlling the relative drive currents to the LED packages.

FIG. 18F illustrates two connection schemes for each of the differenttypes of LED packages included in the tunable troffer light fixture ofFIG. 18A.

FIGS. 19A-19C are schematic diagrams illustrating layout arrangementsand connection schemes for the different types of LED packages includedin light fixtures according to further embodiments of the presentinvention.

FIG. 20A is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating a range of color points that may be achieved using amodified version of the tunable troffer light fixture of FIG. 18A thathas an extended tuning range.

FIGS. 20B and 20C are graphs comparing the lumen per watt and CRIperformance of the tunable troffer light fixture of FIG. 18A and themodified version thereof that has the extended tuning range illustratedin FIG. 20A.

FIG. 20D is a graph illustrating the change in current for various LEDstrings of the tunable troffer light fixtures of FIG. 18A and FIG. 20Awhen the light fixtures are driven to operate in each of the five colorpoint regions illustrated in FIG. 18C.

FIG. 21A is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating a range of color points that may be achieved using afurther modified version of the tunable troffer light fixture of FIG.18A that has a different extended tuning range.

FIG. 21B is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating how the techniques according to embodiments of the presentinvention may be used to provide a light fixture that is tunable over awider range of color temperatures.

FIG. 22A is a plan view of a tunable troffer light fixture according tofurther embodiments of the present invention with a call-outillustrating the arrangement of the LED packages included therein ingreater detail.

FIG. 22B is a graph illustrating the intensity of the radiation emittedas a function of wavelength for the tunable troffer light fixture ofFIG. 22A when operated to fall within the E3 through E7 color bins alongwith comparative data for a different light fixture design.

FIG. 23 is a plan view of an alternative printed circuit board that maybe used in the light fixture of FIG. 22A.

FIG. 24 is a plan view of a printed circuit board according to furtherembodiments of the present invention.

FIGS. 25A-25B illustrate printed circuit boards for solid state lightfixtures according to further embodiments of the present invention thathave three different types of LED packages arranged in patterns that mayprovide improved color mixing.

DETAILED DESCRIPTION

The present invention is directed to solid state light fixtures thatemit white light that are suitable for high temperature operation. Theselight fixtures include both LEDs that have recipient luminophoricmediums that include yellow and/or green light emitting phosphors aswell as LEDs that have recipient luminophoric mediums that include redlight emitting phosphors. The solid state light fixtures according toembodiments of the present invention may exhibit high luminousefficiency levels while providing excellent color rendering performanceand may maintain high levels of performance when the LEDs includedtherein are operating at elevated temperatures such as temperatures of80° C. or 90° C. or 100° C. or more.

As used herein, the term “solid state light fixture” refers to apackaged lamp, light bulb or other light fixture (e.g., ceiling mounted“troffer” light fixtures that are used as replacement for conventionalfluorescent light fixtures) that include a plurality of LEDs. The LEDsmay comprise, for example III-V nitride (e.g., gallium nitride) basedLEDs that are fabricated on a silicon carbide, sapphire or galliumnitride substrates such as various devices manufactured and/or sold byCree, Inc. of Durham, N.C. Such LEDs may (or may not) be configured tooperate such that light emission occurs through the growth substrate (ora semiconductor layer that was near the growth substrate if the growthsubstrate is removed) in a so-called “flip chip” orientation. The LEDsmay be vertical devices with a cathode contact on one side of the LED,and an anode contact on an opposite side of the LED, or may be lateraldevices in which both contacts are on the same side of the device. Thedesign and fabrication of LEDs are well known to those skilled in theart, and hence further description thereof will be omitted.

Visible light may include light having many different wavelengths. Theapparent color of visible light can be illustrated with reference to atwo-dimensional chromaticity diagram, such as the 1931 CIE ChromaticityDiagram illustrated in FIG. 1. Chromaticity diagrams provide a usefulreference for defining colors as weighted sums of colors.

As shown in FIG. 1, colors on a 1931 CIE Chromaticity Diagram aredefined by x and y chromaticity coordinates that fall within a generallyU-shaped area. Colors on or near the outside of the area are saturatedcolors composed of light having a single wavelength, or a very smallwavelength distribution. Colors on the interior of the area areunsaturated colors that are composed of a mixture of light of differentwavelengths. White light, which can be a mixture of light of manydifferent wavelengths, is generally found near the middle of thediagram, in the region labeled 10 in FIG. 1. There are many differenthues of light that may be considered “white,” as evidenced by the sizeof the region 10. For example, some “white” light, such as lightgenerated by sodium vapor lighting devices, may appear yellowish incolor, while other “white” light, such as light generated by somefluorescent lighting devices, may appear more bluish in color.

A binary combination of light from light sources emitting light of firstand second colors may appear to have a different color than either ofthe two constituent colors. The color of the combined light may dependon the wavelengths and relative intensities of the two light sources.For example, light emitted by a combination of a blue source and a redsource may appear purple or magenta to an observer. Similarly, lightemitted by a combination of a blue source and a yellow source may appearwhite to an observer.

Each point in the graph of FIG. 1 is referred to as the “color point” ofa light source that emits a light having that color. As shown in FIG. 1a locus of color points that is referred to as the “black-body” locus 15exists which corresponds to the location of color points of lightemitted by a black-body radiator that is heated to various temperatures.The black-body locus 15 is also referred to as the “planckian” locusbecause the chromaticity coordinates (i.e., color points) that lie alongthe black-body locus obey Planck's equation: E(λ)=Aλ⁻⁵/(e^(B/T)−1),where E is the emission intensity, λ is the emission wavelength, T isthe color temperature of the black-body and A and B are constants. Colorcoordinates that lie on or near the black-body locus 15 yield pleasingwhite light to a human observer.

As a heated object becomes incandescent, it first glows reddish, thenyellowish, and finally bluish with increasing temperature. This occursbecause the wavelength associated with the peak radiation of theblack-body radiator becomes progressively shorter with increasedtemperature, consistent with the Wien Displacement Law. Illuminants thatproduce light which is on or near the black-body locus 15 can thus bedescribed in terms of their correlated color temperature (“CCT”). Asused herein, the term “white light” refers to light that is perceived aswhite, is within 7 MacAdam ellipses of the black-body locus on a 1931CIE chromaticity diagram, and has a CCT ranging from 2000K to 10,000K.White light with a CCT of 4000K may appear yellowish in color, whilewhite light with a CCT of 8000K or more may appear more bluish in color,and may be referred to as “cool” white light. “Warm” white light may beused to describe white light with a CCT of between about 2500K and4500K, which is more reddish or yellowish in color. Warm white light isgenerally a pleasing color to a human observer. Warm white light with aCCT of 2500K to 3300K may be preferred for certain applications.

The ability of a light source to accurately reproduce color inilluminated objects is typically characterized using the color renderingindex (“CRT”). The CRT of a light source is a modified average of therelative measurements of how the color rendition of an illuminationsystem compares to that of a reference black-body radiator whenilluminating eight reference colors. Thus, the CRT is a relative measureof the shift in surface color of an object when lit by a particularlamp. The CRT equals 100 if the color coordinates of a set of testcolors being illuminated by the illumination system are the same as thecoordinates of the same test colors being irradiated by the black-bodyradiator. Daylight generally has a CRT of nearly 100, incandescent bulbshave a CRT of about 95, fluorescent lighting typically has a CRT ofabout 70 to 85, while monochromatic light sources have a CRT ofessentially zero. Light sources for general illumination applicationswith a CRT of less than 50 are generally considered very poor and aretypically only used in applications where economic issues preclude otheralternatives. Light sources with a CRT value between 70 and 80 haveapplication for general illumination where the colors of objects are notimportant. For some general interior illumination, a CRT value ofgreater than 80 is acceptable. A light source with color coordinateswithin 4 MacAdam step ellipses of the planckian locus 15 and a CRT valuethat exceeds 85 is more suitable for general illumination purposes.Light sources with CRT values of more than 90 provide greater colorquality.

For general illumination and various other applications, it is oftendesirable to provide a lighting source that generates white light havinga relatively high CRI, so that objects illuminated by the lightingsource may appear to have more natural coloring to the human eye.Accordingly, such lighting sources may typically include an array ofsemiconductor lighting devices including red, green and blue lightemitting devices. When red, green and blue light emitting devices areenergized simultaneously, the resulting combined light may appear white,or nearly white. However, even light that is a combination of red, greenand blue emitters may have a low CRI, particularly if the emittersgenerate saturated light, because such light may lack contributions frommany visible wavelengths.

While CRI is useful in gauging the color rendering performance of alight source, standing alone, CRI may not always provide a satisfactorymeasure of the color quality. In particular, CRI is an average colorrendering value for eight specific sample colors that are generallyreferred to as R1-R8. These eight color samples R1-R8 are primarilypastel shades, as opposed to saturated colors. As such, light emittingdevices that emit light having high CRI values may still fall short inrendering certain hues such as red hues. For example, the red content ofa light source may be important for accurately rendering colors ofvarious foods, skin tones, wood, furniture and other objects. Only a fewof the color samples used to compute CRI have significant red content(namely sample R1, which is a pink shade, and sample R8, which is apurple shade), and these samples are not saturated color samples. Assuch, high CRI scores may be achieved even without significant redcontent in a light source, and thus a high CRI score may be achieved insome cases even though the light source may not do a good job ofrendering red hues.

In order to address this issue, seven additional color samples, labeledCRI R9-R15, have been defined that measure the color rendering of alight source for either saturated colors (R9-R12, corresponding tosaturated red, yellow, green and blue light) or for other colors(R13-R15) corresponding to two different skin tones and leaf green.These color samples are not used in calculating CRI, which is basedsolely on color samples R1-R8, but may be important when evaluating thecolor rendering of a particular light source. The sample color R9 is thesaturated red color, and it is generally known that the ability toreproduce red colors well is key for accurately rendering colors, as thecolor red is often found mixed into processed colors. Accordingly, allelse being equal, lamps with high R9 values tend to produce the mostvivid colors. Thus, the CRI R9 value of light emitted by a light sourceis also often considered to be an important performance parameter forthe light source.

Since color sample R9 corresponds to a saturated color, there is no wayto achieve a high R9 score without a significant red content in thelight source. This can be seen in FIG. 2, which shows the reflectancespectra (i.e., reflected power as a function of wavelength) for theR1-R9 color samples when illuminated by a reference light source. As canbe seen in FIG. 2, color samples R1-R8 include mixes of many differentcolors, as shown by the fact that samples R1-R8 have significantcontribution across a broad portion of the visible light spectrum,whereas color sample R9 includes very high spectral reflectivity in thered region with virtually no reflectivity below 600 nm. Thus, the R9color sample may provide a very good indicator of a light source'sability to accurately render the color of red objects, and for thisreason is often considered along with CRI in evaluating the quality ofthe color of a light source.

In addition, CRI also confers limited ability to predict colordiscrimination (i.e., to perceive subtle difference in hue) or colorpreference. There appears to be a natural human attraction to brightercolor. Daylight provides a spectrum of light that allows the human eyeto perceive bright and vivid colors, which allows a human observer todistinguish objects having even very subtle color shade differences.Accordingly, it is generally recognized that daylight and blackbodysources are superior to many artificial light sources for emphasizingand distinguishing color. The ability of human vision to differentiatecolor is different under correlated color temperature conditionsproviding the same CRI. Such differentiation is proportional to thegamut area of the illuminating light.

The gamut area of a light source can be calculated as the area enclosedwithin a polygon defined by the chromaticities in CIE 1976 u′v′ colorspace of the eight color samples R1-R8 used to calculate CRI whenilluminated by a test light source. Gamut area index (GM) is aconvenient way of characterizing in chromaticity space how saturated theillumination makes objects appear—with a larger GAI making object colorsappear more saturated. GM is a relative number whereby an imaginaryequal-energy spectrum (wherein radiant power is equal at allwavelengths) is scored as 100. GM for a test source is determined bycomparing color space area of the light being tested to the color spacearea produced by the imaginary or theoretical equal-energy spectrum(EES) source. Unlike CRI, which has a maximum value of 100, GAI canexceed 100, meaning that some sources saturate colors more than anequal-energy source saturates color.

Typical blackbody-like light sources and typical daylight-like lightsources have different gamut areas. Low correlated color temperaturesources (e.g., incandescent emitters) have a GAI of approximately 50%(i.e., about half the gamut area of the EES source). Sources with highercorrelated color temperature values have a larger GAI. For example, avery bluish light with a correlated color temperature of 10000K may havea GAI of 140%.

Another way of characterizing how saturated an illuminant makes objectsappear is relative gamut area, or “Qg”, which is also referred to as the“Color Quality Scale Qg,” which is the area formed by (a*, b*)coordinates of the 15 test-color samples R1-R15 normalized by the gamutarea of a reference illuminant at the same correlated color temperatureand multiplied by 100. In a manner similar to GAI, Qg values can exceed100; however, Qg values are scaled for consistency relative tocorrelated color temperature. Because of chromatic adaptation, andbecause correlated color temperature is selected to set the overallcolor tone of an environment as part of the lighting design process,variable-reference measures such as Qg may be especially relevant toapplied lighting design. If the relative gamut is greater than that ofthe reference, and illuminance is lower than that provided by daylight,then an increase in preference and discrimination might be expectedrelative to the reference at that same correlated color temperature.Conversely, if the relative gamut is smaller than that of the reference,then a decrease in preference and discrimination might be expectedrelative to the reference at the same correlated color temperature.

High Qg values are generally associated with more vivid colors. It isbelieved that, in at least certain contexts, some consumers may preferlight sources with significantly enhanced vividness. It may, however, bechallenging to provide enhanced vividness in combination with highluminous efficacy, and further in combination with reasonably high colorrendering index values.

Another important performance parameter for an LED lighting source isthe intensity of the light emitted, which is referred to as the radiantflux of the device. However, as the human eye has varying sensitivity todifferent wavelengths of light, the intensity of the light emitted by alighting source is most typically measured in terms of the lightingsource's “luminous flux,” which is a measure of the power of the lightemitted by a light source as perceived by a human observer. The luminousflux of a light source is typically measured in lumens (lm). Theluminous flux of a light source differs from the radiant flux of thelight source in that the radiant flux measures the total power emitted,while the luminous flux weights the power of the light emitted at eachwavelength based on a luminosity function which represents the responseof the human eye for each different wavelength.

FIG. 3 is a graph of the above-referenced luminosity function thatcorresponds to the response of the human eye to light in the visiblelight spectrum. As shown in FIG. 3, the human eye cannot perceive lightat wavelengths below about 400 nm and above about 700 nm. The maximumresponse of the human eye to light occurs at about 555 nm. Incalculating luminous flux, the radiant flux of a light source isweighted based on the eye sensitivity curve of FIG. 3. As the amount oflight emitted by an LED is generally a function of the power input tothe LED, the luminous flux performance of semiconductor light emittingdevices are typically compared with each device being driven at the sameinput power level or, alternatively, the devices may be compared interms of the luminous flux per unit of input power (e.g., lumens perWatt) that each device emits at the input power level for which eachdevice is designed to operate.

Because of the varying sensitivity of the human eye to light ofdifferent wavelengths, there tends to be a tradeoff between the luminousflux of the light emitted by an LED lighting source and the CRI of thelight emitted. For example, since the human eye is most sensitive tolight at a wavelength of about 555 nm, a monochromatic light source at555 nm would exhibit a high luminous flux value. However, in order toobtain high CRI values, it is generally necessary to have lightcontribution across a wide range of wavelengths, including wavelengthsthat are relatively far away from 555 nm where the peak sensitivity oflight to the human eye occurs. This is particularly true with respect toCRI R9 performance which is a measure of color rendering in the redcolor range. Because the human eye has reduced sensitivity to thewavelengths on either end of the visible light spectrum, the lightcontributions that are often added to improve the CRI of a device mayresult in a decrease in the luminous efficiency of the device.

As will be described in greater detail below, solid state light fixturesaccording to embodiments of the present invention include LEDs andassociated recipient luminophoric mediums that include phosphors thathave peak emission wavelengths in various color ranges. For purposes ofthis disclosure, the various color ranges of visible light are definedas shown in TABLE 1 below. It will be appreciated, however, that thereare not sharp boundaries between different colors of the spectrum. Forexample, light having wavelengths from 430-450 nm may appearblue-violet, while light having wavelengths from 540-560 nm may appearyellow-green, etc.

TABLE 1 Color Wavelength Range (nm) Blue 430-479 Cyan 480-510 Green511-549 Yellow 550-580 Orange 581-604 Red 605-700

An LED or phosphor that emits light having a peak wavelength in one ofthe above color ranges may be referred to with reference to the colorrange. By way of example, a phosphor that emits light having a peakwavelength of 630 nm may be referred to herein as a “red phosphor,”while a phosphor that emits light having a peak wavelength of 535 nm maybe referred to as a “green phosphor.”

There is a demand for solid state light fixtures such as, for example,solid state light bulbs that look and feel to a consumer like aconventional incandescent light fixture or bulb. This demand tends toplace limits on the size and form factor of solid state light fixtures.Moreover, cost is a critical constraint for many solid state lightfixtures.

One potential issue with solid state light fixtures is heat generation.While a solid state light bulb (or other fixture) typically is farcooler under steady-state operation than an incandescent light bulb thatgenerates a similar amount of light, the LEDs themselves are driven atcurrents that are sufficient to cause the LEDs to heat up to fairly hightemperatures such as temperatures in excess of 100° C. While the heatproduced by incandescent sources is generally radiated away as infraredemission, the heat produced by LEDs is concentrated at the chip/packagelevel and needs to be removed through conduction, using thermallyconductive heat sinks. Unfortunately, with respect at least to the typesof LEDs that are typically used in light fixtures, the performance ofthe LED tends to decrease with increasing operating temperature,resulting in reduced luminous flux and reduced reliability as theexpected lifetime of an LED may decrease when operated at highertemperatures. Accordingly, heat generation in solid state light fixturesmay be a significant concern.

In order to mitigate the problems caused by heat generation, solid statelight fixtures often include physical structures such as heat sinks thatare designed to vent the heat that is generated during operation of theLEDs away from the LEDs and, in some embodiments, to outside the solidstate light fixture. These heat sinks typically are formed of metal orother materials that have high thermal conductivity and may be designedto provide pathways for transferring heat that builds up in the vicinityof the LEDs to outside the light fixture. For larger footprintapplications such as T8 tubes or troffers, another thermal managementapproach may be used to prevent elevated LED temperatures. Inparticular, in such larger footprint applications, spatially dispersed(distributed) LED sources may be used where more numerous LEDs run atlower power and therefore locally produce a lower heat load and hencelower LED operating temperatures. When solid state light fixturesinclude heat sinks or distributed LED designs, it is typically possibleto maintain the temperature of the LEDs at relatively low levels (e.g.,below 80° C.) where the LEDs may exhibit high luminous output and longexpected operating lifetimes.

Unfortunately, the inclusion of heat sinks typically increases thefabrication cost of an LED light bulb, and may also tend to make thesolid state light bulb look less like a traditional incandescent lightbulb. Thus, it may be desirable to use smaller heat sinks in solid statelight fixtures or forego the use of such heat sinks altogether. However,when smaller heat sinks are employed or the heat sinks are omittedaltogether, the steady-state expected operating temperature of the LEDsmay increase significantly. Also, a light bulb by its specified shapeand lumen level is not a distributed light source design. For example,for a 60 Watt equivalent solid state light fixture that is implementedin a package that is roughly equivalent in size and shape to aconventional A19 incandescent light bulb with a minimal heat sink, thesteady-state operating temperatures of the LEDs included in the devicewill typically be near 100° C. At these temperatures, luminous flux,reliability and color rendering of the LEDs may all be concerns, makingit difficult to fabricate solid state light bulbs that provideacceptable performance.

Pursuant to embodiments of the present invention, solid state lightfixtures are provided that may exhibit improved performance when theLEDs thereof are operating at higher temperatures such as, for example,temperatures of 80° C., 90° C. or 100° C. or more. These solid statelight fixtures may include a plurality of blue-shifted-yellow and/orblue-shifted-green LED packages as well as a plurality ofblue-shifted-red LED packages. Herein, the term “blue-shifted-yellow LEDpackage” refers to an LED that emits light in the blue color range thathas an associated recipient luminophoric medium that includesphosphor(s) that receive the blue light emitted by the blue LED and inresponse thereto emit light having a peak wavelength in the yellow colorrange. A common example of a blue-shifted-yellow LED package is aGaN-based blue LED that is coated or sprayed with a recipientluminophoric medium that includes a YAG:Ce phosphor. Similarly, as usedherein the term “blue-shifted-green LED package” refers to an LED thatemits light in the blue color range that has an associated recipientluminophoric medium that includes phosphor(s) that receive the bluelight emitted by the blue LED and in response thereto emit light havinga peak wavelength in the green color range, and the term“blue-shifted-red LED package” refers to an LED that emits light in theblue color range that has an associated recipient luminophoric mediumthat includes phosphor(s) that receive the blue light emitted by theblue LED and in response thereto emit light having a peak wavelength inthe red color range. In some cases, a recipient luminophoric medium thatis associated with a blue LED may include, for example, both green andyellow phosphors. In such a case, if the peak wavelength of the combinedlight output by the green and yellow phosphors is in the yellow colorrange, the LED is considered to be a blue-shifted-yellow LED package,whereas if the peak wavelength of the combined light output by the greenand yellow phosphors is in the green color range, the LED is consideredto be a blue-shifted-green LED package. Herein the term“blue-shifted-yellow/green LED package” refers to a phosphor convertedblue LED where the phosphor particles have a peak wavelength in eitherthe green or yellow color ranges.

Before describing the solid state light fixtures according toembodiments of the present invention in further detail it is helpful todiscuss the approaches that have most often been employed conventionallyto implement high luminous output solid state light bulbs that may beused as replacements for 40, 60, 75 and 100 Watt incandescent lightbulbs.

Under the first conventional approach, light fixtures are provided thatcombine blue-shifted-yellow and/or blue-shifted-green LED packages withred LEDs which are typically AlInGaP based LEDs. These light fixturesmay emit white light having excellent color rendering properties. Lightfixtures implemented using this approach are sometimes referred to as“true white” solid state light fixtures because of their excellent colorrendering properties. U.S. Pat. No. 7,213,940 discloses various truewhite solid state light fixtures.

Unfortunately, the red LEDs that are traditionally used in such truewhite solid state light fixtures may exhibit reduced efficiency atincreased operating temperatures. For example, FIG. 4 is graphillustrating the emission spectra as a function of operating temperaturefor a “true white” solid state light fixture that includes bothblue-shifted-yellow LED packages and red AlInGaP LEDs. In FIG. 4, curve20 represents the emission spectrum for the true white solid state lightfixture when the LEDs included therein are operating at a steady-stateoperating temperature of 25° C. Curve 22 illustrates the emissionspectrum for the true white solid state light fixture when the LEDsincluded therein are operating at a steady-state operating temperatureof 70° C. As can be seen, at the heightened operating temperature, thetotal output power decreases significantly and the wavelength of thepeak in the red color range shifts to the right (i.e., to longerwavelengths).

As discussed above with reference to FIG. 3, the human eye is lessresponsive to light at these higher wavelengths, which means that theshift to such higher wavelengths may reduce the luminous efficiency ofthe device and change the color of the light as compared to when theLEDs are operated at lower temperatures (such as at the initial turn-onof the light fixture or when in a cooler ambient). In order to addressthis color shift, color control circuitry may be included in true whitesolid state light fixtures that adjusts the relative drive current thatis supplied to the blue-shifted-yellow LED packages as compared to thered LEDs in order to maintain the color point of the device close to adesired value. However, this approach requires additional circuitry,which drives up the manufacturing cost of the light fixture andpotentially increases the size of the light fixture, and this approachmay reduce the luminous efficiency of the device as it typicallyrequires increasing the amount of current supplied to the red LEDs whichare typically less efficient as compared to the blue-shifted-yellow LEDpackages. This gap in performance increases with increasing operatingtemperature.

Moreover, the luminous efficiency of the red AlInGaP LEDs tends to notonly degrade at higher temperature because of the color shift, but alsobecause the power output by the red LEDs decreases with increasedoperating temperature, and does so at a rate that is faster than thecorresponding rate of decrease for the gallium nitride based blue LEDsthat are typically used in the blue-shifted-yellow LED packages. Theluminous flux performance of a sample red AlInGaP LED as compared to asample blue-shifted-red LED package formed using a gallium nitride basedblue LED is illustrated in FIG. 5A. In FIG. 5A, the output of the redLEDs and the blue-shifted-yellow LED packages are self-normalized totheir own flux values at an operating temperature of 25° C. to highlightthe difference in how the performance of these devices changes as afunction of operating temperature. As can be seen in FIG. 5A, theluminous output of the red AlInGaP LED (curve 32) deteriorates at arapid rate with increasing operating temperature, such that at anoperating temperature of 150° C. the luminous output is less than 25% ofthe luminous output at 25° C. In contrast, while the luminous output ofthe blue-shifted-red LED package (curve 30) also decreases withincreasing operating temperature, it does so much more slowly, and at anoperating temperature of 150° C. the luminous output is still about 80%of the luminous output at 25° C. As can also be seen in FIG. 5A, at anoperating temperature of about 100° C., the luminous flux of aconventional red AlInGaP LED is only about 50% of the luminous fluxthereof when operated at 25° C., and the reliability (i.e., expectedoperating lifetime) of red AlInGaP LEDs at such elevated temperaturesmay be significantly reduced. At high operating temperatures (e.g.,temperatures of about 100° C. or more), a blue-shifted-red LED packagemay be brighter and more efficient than a red AlInGaP LED.

As noted above, the other potential problem with the use of red AlInGaPLEDs at higher operating temperatures is the change in the shape of theemission spectra which may occur. FIG. 5B is a graph illustrating thechange in peak wavelength as a function of operating temperature forboth a blue-shifted-red LED package (curve 40) and a red AlInGaP LED(curve 42). As shown in FIG. 5B, the peak wavelength of theblue-shifted-red LED package varies by no more than about 1 nm over anoperating temperature range of 25° C. to 150° C. In contrast, the peakwavelength of the red AlInGaP LED varies by almost 18 nm over thisoperating temperature range, which is what results in the significantshift in the peak wavelength shown in FIG. 4, thereby oftennecessitating electronic control to compensate for this variation.

Thus, because of the need to provide temperature control circuitry aswell as the reduced efficiency of the red AlInGaP LEDs at higheroperating temperatures, true white solid state light fixtures may not bewell-suited for some high temperature applications.

The second conventional approach used to implement high output solidstate light bulbs that may be used as replacements for 40, 60, 75 and100 Watt incandescent light bulbs is to use blue LED packages that haverecipient luminophoric mediums that have multiple phosphors so that thecombined emission of the blue LEDs and the phosphors is a high qualitywhite light. Such LED packages are referred to herein as “phosphorconverted white LED packages.” Conventional phosphor converted white LEDpackages may include, for example, a recipient luminophoric medium thathas a green phosphor and/or a yellow phosphor along with one or more redphosphors.

The present inventors have realized that one potential problem with thissecond approach is that the red phosphors that are often used inphosphor converted white LED packages not only convert the blue lightemitted by the LED, but also tend to consume much of the emission of theyellow and/or green phosphor. This can be seen, for example, withreference to FIGS. 6 and 7. In particular, FIG. 6 is a graphillustrating the absorption spectra (curves 50, 52, 54, 56) for fourdifferent (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor compositions, which is atype of red phosphor that is commonly used in phosphor converted whiteLED packages. FIG. 7 is a graph illustrating the emission spectrum(i.e., the intensity of the radiation emitted as a function ofwavelength) of a conventional phosphor-converted white LED package thatuses a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor in addition to yellow andgreen phosphors.

As shown in FIG. 6, the absorption spectrums for the four example(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors have a broad, somewhat uneven peakthat extends from about 500 nm to about 560 nm. The emission spectra fortypical yellow and green phosphors used in phosphor-converted white LEDpackages typically peak in the 530-565 nm range, which is right in themiddle of the absorption spectra of the (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺phosphor. While the absorption spectra for the(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors are quite broad so that therestill is good absorption in the 450-460 nm range corresponding to thepeak emission wavelength of a representative blue LED, the absorption isreduced by about 20-30 percent at this wavelength range as compared tothe amount of absorption across the broad peak. Moreover, the blue LEDshave a small FWHM widths (e.g., less than 30 nm), while the green andyellow phosphors typically have FWHM widths on the order of 70-120 nm.As a result, the (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors will tend toabsorb relatively less of the light that was emitted by the blue LED andrelatively more of the light that was emitted by the green and/or yellowphosphors.

Phosphors are not fully efficient light emission systems. Consequently,when a phosphor absorbs light emitted by an LED and emits light of alonger wavelength in response thereto, the optical output power of thelight emitted by the combination of the LED and the phosphor will beless than the output power of the light emitted by the LED alone if nophosphor is used. In a conventional phosphor-converted white LEDpackage, the red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor is excited by boththe blue light from the LED as well as by the emission from the yellowand green phosphors that are excited by the blue LED. A substantial(likely a majority) of the light that excites the red phosphororiginates from the conversion of the LED blue light to yellow and greenlight by the yellow and green phosphors. Such double conversion resultsin increased inefficiencies since each conversion has intrinsic opticalloss. One impact of this double conversion can be seen in the emissionspectra of FIG. 7, where the left side of the main emission peak shiftsinwardly at around 550 nm (indicated by 64 in FIG. 7). Such a reductionin spectral output at approximately the peak sensitivity of the humaneye response curve has a negative impact on the luminous efficiency ofthe device.

Additionally, as can also be seen from FIG. 6, the wavelength rangewhere the red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor absorption is thehighest is the 510-545 nm wavelength range, which is the green colorrange. While the red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor also absorbslight fairly strongly in the yellow color range, the red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor also has some degree of emission inthe yellow color range which at least partially offsets this absorption.However, the red (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor has very lowemission in the green color range, and hence emission of the phosphorconverted white LED packages may be reduced in the green color range,which typically acts to reduce the CRI of the device. This effect can becompensated for by adding a green phosphor such as, for example, aLu₃Al₅O₁₂:Ce phosphor (referred to herein as a “LuAG:Ce” phosphor),although the green phosphor tends to be less efficient than the YAG:Ceyellow phosphor, so a tradeoff will typically exist between luminousefficiency and CRI when compensating for the absorption by the red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor of light emitted in the green colorrange.

Pursuant to embodiments of the present invention, solid state lightbulbs are provided that include both blue-shifted-yellow and/orblue-shifted-green LED packages along with blue-shifted-red LEDpackages. By using two (or more) different types of phosphor-convertedblue LED packages instead of phosphor-converted LED packages thatinclude phosphors of both yellow/green and red colors mixed together,the above-described double-conversion inefficiency problem may bereduced or eliminated. Consequently, the solid state light fixturesaccording to embodiments of the present invention may provide improvedperformance as compared to both conventional, state of the art truewhite and phosphor-converted white LED package based light fixtures interms of luminous flux, CRI, CRI R9 and Qg performance, and may also besuitable for use at high operating temperatures. Such a solution thatimproves the performance across the full range of factors that aretypically used to judge the performance of an LED is quite remarkable.Example embodiments of such light bulbs will now be described in greaterdetail with reference to FIGS. 8-14.

FIG. 8 is a graph illustrating the emission spectra of theblue-shifted-green (curve 60) and blue-shifted-red (curve 62) LEDpackages that are included in a solid state light bulb according toexample embodiments of the present invention. As shown in FIG. 8, eachemission spectrum has a small peak at about 450 nm which reflects thepass-through emission of the respective blue LEDs. As shown, the blueLEDs used to form the blue-shifted-green LED packages may have somewhatshorter peak wavelengths than the blue LEDs used to form theblue-shifted-red LED packages. Various reasons why such an approach maybe advantageous in certain embodiments will be described in detailbelow. The blue-shifted-green LED packages have a broad emission peakcentered at about 545 nm, while the blue-shifted-red LED packages have asomewhat narrower (although still quite broad) emission peak centered atabout 625 nm. The locations and shapes of these peaks may be adjusted byselection of the phosphors used in the blue-shifted-green andblue-shifted-red LED packages.

FIG. 9 is a graph illustrating the intensity of the radiation emitted asa function of wavelength of a solid state light fixture according toembodiments of the present invention that includes theblue-shifted-green and blue-shifted-red LED packages that were used togenerate the graph of FIG. 8. As shown in FIG. 9, the combined emissionspectrum has a narrow emission peak at about 450 nm that is attributableto the light from the blue LEDs that passes through the recipientluminophoric mediums without conversion, and a broad emission peak thatis attributable to the two phosphors that have peak wavelengths of about620 nm. This broad emission peak includes a distinct shoulder at about545 nm that has its own sub-peak.

FIG. 10 is a graph comparing the emission spectrum of a solid statelight fixture that has a conventional phosphor-converted white LEDpackage that uses a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor (curve 72 inFIG. 10) to the emission spectrum of a solid state light fixtureaccording to embodiments of the present invention (curve 70 in FIG. 10).As shown in FIG. 10, the two emission spectra are quite similar atwavelengths below about 500 nm and at wavelengths above about 650 nm,but are quite different in the range of about 500-650 nm. In particular,the solid state light fixture according to embodiments of the presentinvention (curve 72) has significantly increased emission in the 500-550nm wavelength range, which results because the red phosphor is no longerabsorbing significant amounts of the light emitted by the yellow and/orgreen phosphors. Because the improved emission is provided atwavelengths corresponding to a region of the eye response curve of FIG.3 where the human eye is highly sensitive to light, the overall resultis that the solid state light fixture according to embodiments of thepresent invention may exhibit approximately the same or even increasedluminous efficacy as compared to a state-of-the-art conventional solidstate light fixture. Moreover, the shape of the emission spectrum mayalso advantageously provide improved color rendering properties in termsof all three of CRI performance, CRI R9 performance and Qg performance.

TABLE 2 compares the luminous flux and color quality performance of fourexample devices according to embodiments of the present invention to aconventional state-of-the-art device. Each device used to generate theperformance data in TABLE 2 consisted of a printed circuit board withtwo LED packages mounted thereon. The data in TABLE 2 was generated bycomparing the performance of two state-of-the-art LED packages in whicha green phosphor, a yellow phosphor and a red phosphor (herein a “BSYGRLED”) were all combined in a single recipient luminophoric medium todevices according to embodiments of the present invention which eachinclude one blue-shifted-yellow/green LED package (also referred toherein as a “BSY/G LED package”) which had both green and yellowphosphors and one blue-shifted-red LED (also referred to herein as a“BSR LED package”). The measurements where performed at room temperatureand the same constant (direct current) drive current for all fivedevices.

TABLE 2 Relative Yellow- Device CCT Luminous Green Red Configuration (K)Flux CRI R9 Qg Phosphor Phosphor 2 BSYGR 2731 100% 83 8 96 1 BSY/G; 2783100% 85 19 100 50% YAG; Red1 1 BSR 50% LuAg 1 BSY/G; 2803  97% 87 33 10150% YAG; Red3 1 BSR 50% LuAg 1 BSY/G; 2775  98% 87 33 102 50% YAG;Red1 + 1 BSR 50% LuAg Red2 1 BSY/G; 2954  99% 89 24 99 20% YAG; Red1 1BSR 80% LuAg

In TABLE 2, “CCT” stands for correlated color temperature, and the“Yellow-Green Phosphor” column lists the relative amounts of yellowphosphor (which is a YAG:Ce phosphor) and green phosphor (which is aLuAG:Ce phosphor) in the recipient luminophoric mediums of the BSY/G LEDpackages used in devices according to embodiments of the presentinvention. Red1 through Red3 refer to three specific red(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors that were used to implement theBSR LED packages. Red1 has an emission peak at 618 nm, Red2 has anemission peak at 629 nm, and Red3 has an emission peak at 624 nm.

As can be seen from TABLE 2, the four devices according to embodimentsof the present invention exhibit improved color rendering as compared tothe conventional state-of-the-art device for all three color renderingmetrics. The CRI R9 performance of the devices according to embodimentsof the present invention are particularly improved, with all fourdevices exhibiting improvements of over 100% in CRI R9 performance, andsome devices providing CRI R9 values that are 3-4 times higher than theconventional device. While the improvements in CRI and Qg are lessdramatic, they are still on the order of 5%, which represents asignificant performance improvement. Moreover, the luminous fluxperformance of the four devices according to embodiments of the presentinvention is comparable to the conventional state-of-the-art device.Moreover, one of the devices (the 50% YAG/50% LuAG with Red1 device)provides matched or improved performance in all four performancecharacteristics evaluated as compared to the conventionalstate-of-the-art device.

In the devices listed in TABLE 2, each BSY/G LED package was implementedby combining a YAG:Ce phosphor and a LuAG:Ce phosphor in the samerecipient luminophoric medium that is excited by a blue LED. However, itwill be appreciated that in other embodiments, separate BSY and BSG LEDpackages may be used to achieve the same effect (i.e., a first blue LEDis provided that has a recipient luminophoric medium having only YAG:Cephosphors included therein and a second blue LED is provided that has arecipient luminophoric medium having only LuAG:Ce phosphors includedtherein). Likewise, each BSR LED package used in the embodiment thatused two red phosphors had both red phosphors combined in the recipientluminophoric medium. However, it will be appreciated that in otherembodiments, two separate BSR LED packages could be used instead, thefirst of which has a recipient luminophoric medium having only the firstred phosphor included therein and the second of which has a recipientluminophoric medium having only the second red phosphor includedtherein. It will also be appreciated that more than two red phosphorsmay be used in other embodiments, and that different green, yellowand/or red phosphors may be used in other embodiments.

While each of the devices listed in TABLE 2 above included both yellowand green phosphors, it will be appreciated that in other embodimentsthe BSY/G LED packages may only include a yellow phosphor or may onlyinclude a green phosphor.

FIG. 11A is a schematic perspective view of a light bulb 100 accordingto embodiments of the present invention with the dome thereof omitted.FIG. 11B is a perspective view of a printed circuit board that isincluded in the light bulb of FIG. 11A that has sevenblue-shifted-yellow/green LED packages and seven blue-shifted-red LEDpackages mounted thereon. FIG. 11C is a cross-sectional view of thelight bulb 100 with a reflector omitted to better show the printedcircuit board. FIG. 11D is a perspective view of an alternativereflector that may be used in the solid state light bulb of FIGS.11A-11C in other embodiments of the present invention.

Referring to FIGS. 11A-11C, the solid state light bulb 100 includes abody 110, a reflector 120, a dome 130 and a submount 140 such as aprinted circuit board. As shown in FIGS. 11A and 11C, the body 110 maybe shaped and sized like the body of a conventional incandescent lightbulb such as an A19 or A21 light bulb. The body 110 may include a pairof electrical contacts 112, 114 that mate with electrical contactstructures of a conventional incandescent light bulb socket. The body110 may include power conversion circuitry (not shown) that converts thealternating current (AC) power received from a light socket to asuitable direct current (DC) voltage that may be used to power the LEDsincluded in solid state light fixture 100. The body 110 may also includeone or more heat sinks 116 that help vent heat generated by the LEDsduring operation to the exterior of the light bulb 100.

The reflector 120 may be mounted to extend upwardly from atop the body110. The reflector 120 may be formed of, for example, a highlyreflective metal or plastic. In the embodiment of FIG. 11A, thereflector 120 includes an annular, truncated frusto-conical shapedreflection surface 122 that is positioned above the printed circuitboard 140. The reflection surface 122 has a central opening 124 thatallows light from LEDs that are positioned in the center of the submount140 to pass through the reflector 120 and emit from the top of the lightfixture 100. The reflector 120 may also have one or more mounting armsthat extend between the reflection surface 122 and the body 110 to holdthe reflection surface 122 in place above the submount 140.

As shown in FIG. 11C, the dome 130 may be mounted atop the body 110 withthe reflector 120 and submount 140 positioned within the interior of thedome 130. The dome 130 may comprise, for example, a plastic or glassdome, and may or may not have the shape of a dome on a conventional A19incandescent light bulb. The dome 130 may comprise a diffuse opticalenclosure. The dome 130 may be designed to mix light emitted by the LEDsincluded in solid state light bulb 100 so that light exiting the dome130 will comprise fully mixed white light.

As shown in FIG. 11B, fourteen phosphor-converted LED packages 142 aremounted on the submount 140. In the depicted embodiment, the submount140 is implemented using a printed circuit board 140. The printedcircuit board 140 may be metal core (MCPCB), a flexible printed circuitboard, or a fiberglass printed circuit board (e.g., FR-4). It will beappreciated that in other embodiments a different submount may be used.For example, a submount formed of aluminum oxide, aluminum nitride,organic insulators, sapphire and/or silicon may be used in otherembodiments. In the solid state light fixture 100 of FIGS. 11A-11C,seven of the LED packages 142 comprise blue-shifted-yellow/green LEDpackages 142A, and the remaining seven LED packages 142 compriseblue-shifted-red LED packages 142B. The LED packages 142 may eachinclude a single LED (i.e., a single LED “chip” or “die”) or multipleLEDs. These LEDs are mounted in the LED package 142, and the LED package142 includes electrical connections to the printed circuit board 140 toprovide electrical power to each LED. In the depicted embodiment, theLED packages 142 are divided into two strings, of seven LED packages 142each, where each string is supplied a 42 volt DC power signal (6 voltsper LED package 142). In some embodiments, the blue-shifted-yellow/greenLED packages 142A may all be part of the first string and theblue-shifted-red LED packages 142B may all be part of the second string.This approach may allow the solid state light bulb 100 to be configuredto have increased red light contribution when the bulb is dimmed, whichcan be achieved by driving the blue-shifted-red LED packages 142B moreheavily than the blue-shifted-yellow/green LED packages 142A when thelight bulb 100 is dimmed. Such a dimming feature may be preferred as itmimics the dimming characteristics of a conventional incandescent lightbulb which comparatively emits more red light when dimmed, as will bediscussed in more detail below.

The LEDs used to form the LED packages 142 can have many differentsemiconductor layers arranged in different ways. LEDs and theirfabrication and operation are generally known in the art and hence areonly briefly discussed herein. The layers of the LEDs can be fabricatedusing known processes such as, for example, metal organic chemical vapordeposition. Typically, LEDs are grown on a growth substrate such as, forexample, a sapphire, silicon carbide, aluminum nitride (AlN), or galliumnitride (GaN) substrate to provide a grown semiconductor wafer, and thiswafer is then singulated into individual LEDs. The growth substrate canremain as part of the final singulated LED or, alternatively, the growthsubstrate can be fully or partially removed. In embodiments where thegrowth substrate remains, it can be shaped and/or textured to enhancelight extraction. The LEDs may be mounted in flip chip configuration insome embodiments.

In the depicted embodiment, each LED package 142 comprises an LED thatis mounted in a lead frame having a cup like cavity, and the recipientluminophoric medium is deposited in this cup-like cavity. The recipientluminophoric medium may comprise an encapsulant material such as, forexample, silicone that has phosphor particles suspended therein. It willbe appreciated that in other embodiments the cavity may be omitted,and/or the recipient luminophoric medium may instead be conformallycoated or sprayed on an upper surface and side surfaces of each LED, ormay be placed in other locations.

In some embodiments, the LED packages 142 may be within an interiorvolume of the diffuse optical enclosure 130, as can be seen, forexample, in FIG. 11C. This is in contrast to many other solid statelight fixtures where the LED packages are positioned outside theinterior volume of an optical enclosure such as, for example, in areflection cavity that has one or more reflective walls that aredesigned to enhance mixing of the light from LED packages that emitdifferent colored light before that light passes into the interiorvolume of an optical enclosure. Because the LED packages 142 accordingto embodiments of the present invention may maintain high efficiency atelevated operating temperatures such as temperatures above 80° C. oreven at temperatures above 90° C. or 100° C., the LED packages 142 maybe located in close proximity to each other which increases colormixing, which allows the LED packages 142 to be mounted within theinterior volume of the dome 130.

In some embodiments, a controller may be included within the body 110.The controller 110 may be configured to increase the relative amount ofdrive current supplied to the blue-shifted-red emitters (i.e., theblue-shifted-red LED packages) as compared to theblue-shifted-yellow/green emitters (i.e., the blue-shifted-yellow/greenLED packages) when the solid state light fixture is dimmed. Conventionalincandescent light bulbs tend to emit light that has increased yellowand red components when dimmed. Since the solid state light bulb 100 hasseparate blue-shifted-yellow/green emitters and blue-shifted-redemitters, the relative drive currents supplied to the blue-shifted-redemitters may be increased as compared to the drive current supplied tothe blue-shifted-yellow/green emitters when the solid state light bulbis dimmed (i.e., when an external control circuit is adjusted to supplyless current to the solid state light bulb). This can be accomplishedby, for example, increasing the relative amount of current supplied toeach blue-shifted-red emitter as compared to the amount of currentsupplied to the blue-shifted-yellow/green emitters when the light bulbis dimmed, or by not supplying current to some of theblue-shifted-yellow/green emitters when the light bulb is dimmed.

In some cases, the correlated color temperature of the light emittedfrom the diffuse optical enclosure may generally decrease with anincreasing level of dimming. Thus, as the luminous flux of the lightbulb decreases, the correlated color temperature may also generallydecrease.

It will also be appreciated that the blue LEDs included in the LEDpackages 142 may or may not have the same peak wavelength. For example,in some embodiments, some of the blue LEDs may be shorter wavelengthblue LEDs (i.e., peak wavelengths between 440 and 455 nm), while otherof the blue LEDs may be longer wavelength blue LEDs (i.e., peakwavelengths between 456 and 480 nm or between 460 and 480 nm). Such anapproach may, for example, approximately double the effective width ofthe pass-through blue light emission, which may help improve the CRIperformance of the light bulb 100. In fact, such an approach may beparticularly helpful as some of the lowest emissions for the light bulbsaccording to embodiments of the present invention may be in the cyancolor range, and the longer wavelength blue LEDs may help fill in thisgap in the emission spectrum. The use of longer wavelength blue LEDsmay, however, result in some reduction in the luminous flux of the solidstate light bulb 100 as the longer wavelength blue LEDs tend to be, onaverage, dimmer than corresponding short wavelength blue LEDs.

The relatively short wavelength blue LEDs may also help achieve higherQg values. However, at very low blue wavelengths, reliability maydecrease as will the efficiency of the emission from the LED in excitingthe yellow and green phosphors. Accordingly, in some embodiments, theshort wavelength blue LEDs may have peak wavelengths in the range ofabout 445 nm to about 455 nm.

In embodiments in which both short and long peak wavelength blue LEDsare used, it may be advantageous to use the longer wavelength blue LEDsin the blue-shifted-red LED packages 142. Referring again to FIG. 6, itcan be seen that one potential disadvantage of using separateblue-shifted-yellow/green and blue-shifted-red LED packages instead ofphosphor converted LED packages which include both yellow/green and redphosphors in the same recipient luminophoric medium is that the amountof red phosphor that is required is typically increased due to the lowerabsorption by the red phosphor in the blue wavelength range as comparedto the green and yellow wavelength ranges. Typically the red phosphorsare more expensive than the green and yellow phosphors, which mayincrease the cost of the light bulb 100. Thus, in selecting the redphosphors, one consideration may be the absorption spectrum of thephosphor, as all else being equal, better absorption in the blue colorrange may be preferred. Additionally, as can be seen in FIG. 6, theabsorption tends to be somewhat better at the longer blue wavelengths,and hence the use of longer blue wavelength LEDs in the blue-shifted-redLED packages 142 may help reduce the overall cost of the light bulb 100.

It should also be noted that the overall efficiency of a red phosphortends to be a function of the Stoke's shift of the phosphor, whichrefers to the difference between the peak wavelength of the lightabsorbed by the phosphor and the peak wavelength of the light emitted bythe phosphor. Generally speaking, the higher the Stoke's shift, thelower the conversion efficiency of the phosphor (the percentage of theincident radiometric optical power that is yielded as down-convertedradiometric optical power). The use of longer wavelength blue LEDs inthe blue-shifted-red LED packages 142 acts to reduce the Stoke's shift,and hence can beneficially improve the conversion efficiency of the redphosphors.

In the solid state light bulb 100 of FIGS. 11A-11C, eachblue-shifted-yellow/green LED package 142 was implemented using a singleblue LED and a recipient luminophoric medium having a 50%/50% mix of aYAG:Ce phosphor and a LuAG:Ce phosphor. Four of the blue-shifted-red LEDpackages 142 were implemented using a single blue LED and the Red1phosphor discussed above with reference to TABLE 2, while the remainingthree blue-shifted-red LED packages 142 were implemented using a singleblue LED and the Red2 phosphor discussed above with reference to TABLE2. The performance of the solid state light bulb 100 was then measuredand compared to the performance of a conventional state-of-the-art solidstate light bulb that included fourteen BSGYR LED packages. The measuredperformance of these devices are shown in TABLE 3 below. The bulbs wereallowed to come to thermal equilibrium in room temperature ambient. Theresulting LED operating temperature was ˜100° C.

TABLE 3 Device CCT Luminous Configuration (K) Flux L/W ccx ccy CRI R9 14BSYGR 2813 811.6 90.6 0.4494 0.4059 81.2 3.8 7 BSY/G; 2812 842.3 97.40.4553 0.4168 84.3 20.1 4 BSR1; 3 BSR2

As shown in TABLE 3, a solid state light bulb according to embodimentsof the present invention provides a significant performance advantage ascompared to the conventional state-of-the-art light bulb. In particular,significant improvement is provided in terms of both the luminous fluxand the lumens-per-Watt performance of the light bulb, while the deviceat the same time achieves an improvement in CRI along with a significantimprovement in CRI R9 performance. While the Qg performance of thedevices was not measured, it is anticipated that a significantimprovement in Qg performance will also be achieved due to the highercontribution of saturated red color as reflected by the significantlyenhanced CRI R9 value.

TABLE 4 compares the luminous flux and color quality performance of asubmount printed circuit board, as shown in FIG. 11B, according toembodiments of the present invention to a submount with conventionalBSYGR LED packages as a function of operating temperature.

TABLE 4 Operating Lumi- Device Temp CCT nous Configuration (° C.) (K)LPW Flux CRI R9 Separate 25 2793 136.9 1123 86.7 35.7 BSY/G and BSRConventional 25 2764 132.8 1092 82.6 7.7 BSYGR Separate 40 2794 135.21097 86.3 34.2 BSY/G and BSR Conventional 40 2768 131.0 1067 82.3 6.6BSYGR Separate 60 2798 132.1 1058 85.8 32.3 BSY/G and BSR Conventional60 2777 127.8 1029 82.8 8.6 BSYGR Separate 85 2810 127.7 1010 85.2 29.7BSY/G and BSR LEDs Conventional 85 2794 122.9 976 82.1 6.0 BSYGRSeparate 100 2808 122.2 960 84.8 28.5 BSY/G and BSR Conventional 1002809 119.0 938 81.5 4.2 BSYGR

As shown in TABLE 4, the submount according to embodiments of thepresent invention provides improved performance at all operatingtemperatures examined. At the target operating temperature of 100° C.(and all other operating temperatures investigated), superior luminousflux and luminous efficiency are provided, as well as improved CRI andCRI R9 performance. In each case, the LED packages were driven by a 100mA current that is a typical driving current for a 60 W incandescentlight bulb replacement.

FIG. 11D is a perspective view of an alternative reflector 120′ that maybe used in place of the reflector 120 in the solid state light bulb 100of FIGS. 11A-11C in other embodiments of the present invention. As shownin FIG. 11D, the alternative reflector 120′ includes a base 124 and aprimary reflection surface 122′. A lower edge 125 of the base 124 may bemounted on the printed circuit board (or other submount) 140 or may bemounted on the body 110 through, for example, openings in the printedcircuit board 140. The reflection surface 122′ may be positioned abovethe printed circuit board 140 within the dome 130. At least oneblue-shifted-yellow/green emitter 142A and at least one blue-shifted-redemitter 142B may be within an internal cavity 126 defined by the base124. Others of the blue-shifted-yellow/green emitters 142A and of theblue-shifted-red emitters 142B may be positioned on the printed circuitboard 140 to surround an external periphery of the base 124.

FIG. 11E is a cross-sectional view of a solid state light bulb 100′according to further embodiments of the present invention. The solidstate light bulb 100′ is very similar to the solid state light bulb 100of FIGS. 11A-11C, except that the reflector 120 is omitted in solidstate light bulb 100′ and is replaced instead with a partiallyreflective/transmissive coating (or other partially reflective materialand/or optical element) 132 that is coated on the dome 130 that reflectsa portion of the light emitted by the LED packages 142 downwardly andoutwardly. It will be appreciated that the partially reflective coating132 may be on the inside of the dome 130, on the outside of the dome 130and/or integrated into the dome material. Instead of, or in addition to,the partially reflective coating 132 the shape of the dome 130 could bemodified to help distribute the light in a desired manner such as, forexample, to meet Energy Star requirements. As one example, a dimplecould be created at the top of the dome 130 that would redirect thelight from the LED packages 142 in a desired direction. In suchembodiments, the dome 130 may or may not include the partiallyreflective coating 132. In still other embodiments, the coating 132could be fully reflective. In such embodiments, the coating may have asmaller surface area and/or may have openings to allow some light topass through. In yet other embodiments, the coating 132 may be diffuseand/or may have different or variable reflective or opticalcharacteristics. The coating/material 132 may provide a desired lightdistribution with uniform color characteristics. The techniquesaccording to embodiments of the present invention may be particularlywell-suited for solid state light bulbs such as A series light bulbs(e.g., A19 and A21 bulbs) and for candelabra light bulbs. These lightbulbs have small form factors which tend to require that the LEDpackages be located in close proximity to each other. The closer the LEDpackage spacing, the more heat that will build up in the vicinity of theLEDs included therein. As discussed above, the luminous flux andefficiency of LEDs typically decreases with increasing operatingtemperature, and hence thermal performance may be a significant issuewith respect to solid state light bulbs, particularly if cost and/orform factor concerns allow the use of minimal heat sink structures, andmay also limit or preclude the use of temperature control circuitry.

As noted above, according to embodiments of the present invention, theuse of blue-shifted-red LED packages may alleviate some of the thermalissues as blue-shifted red LED packages may exhibit higher luminous fluxperformance and more stable color rendering performance as compared tothe red AlInGaP LEDs that are conventionally used in many solid statelight fixtures. Moreover, with the use of both blue-shifted yellow/greenand blue-shifted-red LED packages, the same type of LED may be used ineach (e.g., a blue gallium nitride based LED). Consequently, the LEDsused to form both the blue-shifted-yellow/green emitters and theblue-shifted-red emitters may degrade at approximately the same rateover time, and hence the color of the combined light emitted by thesolid state light fixtures according to some embodiments of the presentinvention may remain relatively consistent as the solid state lightfixture ages. This may allow for the provision, in some embodiments, ofsolid state light fixtures that do not include control circuitry thatadjusts the relative amount of drive current supplied to theblue-shifted-yellow/green emitters as compared to the blue-shifted-redemitters in order to compensate for different rates in degradation ofthe LEDs included in such emitters. Such control circuitry is typicallyprovided in solid state light fixtures that use AlInGaP LEDs toimplement the red emitters.

A problem that arises, however, when using separateblue-shifted-yellow/green and blue-shifted-red LED packages in a smallform factor light fixture such as an A series light bulb is that thereis reduced space for mixing the colors of the separate yellow/green andred emitters. If the color mixing is inadequate, the combined lightoutput exiting the light bulb may appear as white light with visiblefringe regions of red, yellow, green or other color emission due todiffraction. Such light is generally not considered acceptable by manyconsumers, as consumers tend to prefer light that mimics the moreuniform light output by conventional incandescent light bulbs. Suchcolor mixing concerns generally are not present when phosphor convertedwhite LED packages are used as such LEDs include the red and greenand/or yellow phosphors in the same recipient luminophoric mediumallowing for mixing of the light at the LED. The use of separateblue-shifted-yellow/green emitters and blue-shifted-red emitters iscounter-intuitive in small form-factor solid state light fixtures suchas A-series light bulbs and candelabra light bulbs, as the operatingtemperature issues tends to require spacing the LED packages furtherapart and this increased spacing and the small size of the diffuseoptical enclosure tends to not allow for sufficient color mixing, whichis why each LED package includes all of the phosphors so that each LEDpackage emits white light.

Pursuant to embodiments of the present invention, solid state lightfixtures such as solid state light bulbs are provided that use varioustechniques to provide improved color mixing so that the non-white lightemitted by the separate blue-shifted-yellow/green and blue-shifted-redLED packages will combine to provide substantially uniform white lightwhen exiting the light bulb. As discussed above with respect to theembodiment of FIGS. 11A-11C, these techniques may include the use ofreflective structures that enhance color mixing and the separateblue-shifted-yellow/green and blue-shifted-red LED packages are arrangedwithin the light bulb to enhance color mixing. Additionally, pursuant tofurther embodiments of the present invention, multi-zone emitters inwhich light having two distinct colors is output from an individual LEDpackage may be used so that enhanced color mixing will occur.

For example, in some embodiments of the present invention, LED packagesare provided that include multiple cavities or regions which may receiverespective recipient luminophoric mediums. These LED packages may beused, for example, in place of the LED packages 142A, 142B that areshown in FIG. 11B. One such example LED package 200 is illustrated inFIGS. 12A-12B. As shown in FIG. 12A, the LED package 200 is providedthat includes two LEDs 220 that are mounted on a submount 210. While twoLEDs 220 are included in the example package of FIGS. 12A-12B, it willbe appreciated that more or fewer LEDs 220 may be provided. The submount210 includes a cavity 214 that is defined by a plurality of sidewalls212. The LEDs 220 may be mounted in the cavity 214.

A divider 230 is provided that divides the cavity 214 into first andsecond sub-cavities 232, 234. A first recipient luminophoric medium 240may be deposited in the first sub-cavity 232 and a second recipientluminophoric medium 242 may be deposited in the second sub-cavity 234.The second recipient luminophoric medium 242 may be different from thefirst recipient luminophoric medium 240. In some embodiments, the firstrecipient luminophoric medium 240 may include a Y₃Al₅O₁₂:Ce phosphorand/or a Lu₃Al₅O₁₂:Ce phosphor, and the second recipient luminophoricmedium 242 may include at least one (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphoror other phosphor that emits light having a peak wavelength in the redcolor range.

The divider 230 may be advantageous as it allows separating the firstand second recipient luminophoric mediums 240, 242 into separatesub-cavities 232, 234, which can reduce or prevent the second recipientluminophoric medium 242 from absorbing light emitted by the firstrecipient luminophoric medium 240, and vice versa. Thus, theabove-described situation where a red phosphor absorbs a significantamount of the emission from a green phosphor and/or from a yellowphosphor may be avoided. Moreover, by having the first and secondrecipient luminophoric mediums 240, 242 in very close proximity and, infact, within the same cavity 214 of a surface mount LED package, themixing between the light emitted from the first and second recipientluminophoric mediums 240, 242 may be improved so that the device willemit light having a more uniform white color.

In some embodiments, the submount 210 may comprise a leadframe. As knownto those of skill in the art, a leadframe refers to a cuplike structurein which one or more LEDs may be mounted and electrically connected to apower source. The cuplike structure may include reflective sidewallsthat help light emitted from the LEDs to escape from the leadframe. Thecuplike structure of the leadframe may define a cavity such as thecavity 214 described above. The cavity may include one or more recipientluminophoric mediums.

In leadframe-based LED packages according to certain embodiments of thepresent invention, the leadframe 210 may include a molded structureformed of, for example, a reflective white plastic that forms thesidewalls 212 that define the cavity 214. The divider 230 may comprisean integral portion of the molded structure (i.e., the structure thatforms the cavity 214 and the sub-cavities 232, 234 may be a singlemolded package structure that has multiple cavities). Alternatively, thedivider 230 may comprise a structure that is separate from the structurethat includes the sidewalls 212 that define the cavity 214. Thisseparate divider 230 may be dispensed or otherwise formed or depositedwithin the cavity 214. The divider 230 may be produced out of white,highly reflective material such as a silicone. The separate divider 230may divide the cavity 214 into the first and second sub-cavities 232,234.

In further embodiments, the submount structure 210 may comprise aceramic or metal submount. In some embodiments, the submount structuremay include a molded structure that is formed on the top surface of theceramic or metal submount. The molded structure may be formed, forexample, by overmolding and/or by dispensing a material such as, forexample, a reflective white plastic onto the ceramic or metal submountto define the cavity 214. The molded structure may include an integraldivider that divides the cavity 214 into multiple sub-cavities such asthe sub-cavities 232, 234. One or more LEDs 220 may be mounted in theceramic submount LED package. The first and second recipientluminophoric mediums 240, 242 may be deposited in the respectivesub-cavities 232, 234 to be in close proximity to each other but to notbe substantially mixed together. A silicone lens may be overmolded overthe LEDs 220.

While FIGS. 12A-12B illustrate one example submount that includes acavity that is divided into two sub-cavities, it will be appreciatedthat in further embodiments additional submounts may be provided thathave a main cavity and divider that divide the main cavity intodifferent numbers of sub-cavities, which may each have the same size ordifferent sizes, and that the same or different recipient luminophoricmediums may be deposited into each such sub-cavity. It will also beappreciated that the divider that is used to divide the cavity definedby the submount into separate sub-cavities may be a separate structureor may be part of the submount structure (e.g., the walls that definethe cavity and the divider that divides the cavity into sub-cavities mayall comprise a single molded structure). In further embodiments adivider may be provided even if there is no cavity, and the first andsecond recipient luminophoric mediums may be sprayed onto the LEDs andonto the submount on the respective sides of the divider. The dividermay act to separate the first and second luminophoric mediums to reduceor prevent them from mixing together.

FIG. 13 is a schematic side view of an LED package 300 according tofurther embodiments of the present invention. As shown in FIG. 13, theLED package 300 includes a submount 310 that has a pair of LEDs 320A,320B mounted thereon. The submount 310 may comprise, for example, aceramic, semiconductor or metal substrate. The LEDs 320A, 320B may bemounted on the substrate 310 in a conventional manner and may beelectrically connected to a power source in a conventional manner.Accordingly, further description of the submount 310 and the electricalconnections will be omitted here. After the LEDs 320A, 320B are mountedon the submount 310, the LED 320A (and perhaps certain other portions ofthe submount 310) may be covered by a mask or stencil, and then a firstrecipient luminophoric medium 322A may be deposited on the submount 310and the exposed LED 320A via any appropriate deposition process such as,for example, spraying. Thereafter, the mask/stencil may be removed and asecond mask/stencil may be placed or formed over the LED 320A (andperhaps certain other portions of the submount 310). Then a secondrecipient luminophoric medium 322B may be deposited on the submount 310and the second (now exposed) LED 320B via any appropriate depositionprocess such as, for example, spraying. The first recipient luminophoricmedium 322A may include yellow and/or green phosphors and may notinclude any red phosphors, and the second recipient luminophoric medium322B may include one or more red phosphors and may not include anyyellow or green phosphors. In this manner, an LED package 300 may beformed that has two distinct emitters that emit different color light.The two emitters may be in very close proximity. For example, the LEDs320A and 320B may be separated by between, for example, 1-50 millimetersin some embodiments. A divider 330 may be provided between the LEDs320A, 320B on the submount 310. The divider 330 may reduce the amount oflight emitted by the LED 320A and the recipient luminophoric medium 322Athat is absorbed by the LED 320B and the recipient luminophoric medium322B, and vice versa, and hence may reduce the amount ofdouble-conversion that may occur. A lens (not shown) may be placed overboth LEDs 320 in some embodiments.

FIG. 14 is a schematic side view of a packaged LED 400 according tostill further embodiments of the present invention. As shown in FIG. 14,the packaged LED 400 includes a submount 410 that has a pair of LEDs420A, 420B mounted thereon. The submount 410 may comprise, for example,a ceramic, semiconductor or metal substrate. The LEDs 420 may be mountedon the substrate 410 in a conventional manner and may be electricallyconnected to a power source in a conventional manner. Accordingly,further description of the submount 410 and the electrical connectionswill be omitted here. The LEDs 420 may comprise, for example, a firstblue-shifted-yellow or a blue-shifted-green LED 420A and a secondblue-shifted-red LED 420B. The LEDs 420A and 420B may be in very closeproximity. For example, the LEDs 420A and 420B may be separated bybetween, for example, 1-50 millimeters in some embodiments. The LEDs420A and 420B may have respective recipient luminophoric mediums 422A,422B formed thereon after the LEDs 420A, 420B are mounted on thesubmount 410. For example, the respective recipient luminophoric mediums422 may be deposited on the LEDs 420 after the LEDs 420 are mounted onthe submount 410 using, for example, a phosphor spraying technique. Inthis case, the recipient luminophoric mediums 422 may extend onto thesidewalls of the LEDs 420 as shown in FIG. 14. In other embodiments, therecipient luminophoric mediums 422 may be deposited on the LEDs 420after the LEDs are singulated but before they are mounted on thesubmount 410 by, for example, mounting the LEDs 420 on a temporarysubmount such as, for example, a tape (not shown), and performing aphosphor spraying process. The phosphor coated LEDs 420 may then bemounted on the submount 410. Alternatively, the recipient luminophoricmediums 422 may be applied using a wafer level deposition process suchas spin-coating or electrophoretic deposition in order to deposit therecipient luminophoric mediums 422 on LED wafers before the wafers arediced into individual LED chips 420.

As shown in FIG. 14, the LED package 400 may not include a cavity suchas the cavity 214 of LED package 200, since the recipient luminophoricmediums 422 were formed on the LEDs 420 prior to placement of the LEDs420 on the submount 410. The LED package 400 may optionally include adivider 430, which may comprise, for example, a reflective plasticdivider 430. Such a divider may reduce the amount of light emitted bythe LED 420A and the recipient luminophoric medium 422A that is absorbedby the LED 420B and the recipient luminophoric medium 422B (and viceversa), and hence may reduce the amount of double-conversion that mayoccur. A lens (not shown) may be placed over both LEDs 420 in someembodiments.

The LED package 400 may exhibit excellent color mixing properties as theseparate blue-shifted-yellow or blue-shifted-green LED 420A and theblue-shifted-red LED 420B are in very close proximity to each other.

The LED packages 200, 300 and 400 that are described above withreference to FIGS. 12A-14 comprise multi-zone emitters in that a singleLED package emits light of two distinct colors. The light of twodistinct colors may be a first color that is on a first side of theblack body locus and a second color that is on a second side of theblack body locus. In some embodiments, the light emitted by the firstzone may comprise blue-shifted-yellow or blue-shifted-green light thatis non-white light that comprises pass through light from a blue LED andlight emitted by yellow and/or green phosphors. The light emitted by thesecond zone may comprise blue-shifted-red light that is non-white lightthat comprises pass-through light from a blue LED and light emitted byone or more red phosphors. In some embodiments, the first and/or thesecond zone may include one or more narrow band phosphors, such as, forexample, K₂SF₆, among others, as disclosed in U.S. Provisional PatentApplication Ser. Nos. 62/222,382 and 62/181,249, each of which areincorporated herein by reference. The light of two different colors maymix well, even when the LED packages 200, 300 and 400 are used insmaller solid state light fixtures, because the two zones that emitlight of different colors are so close together. A plurality of the LEDpackages 200, 300 and/or 400 may be included in the solid state lightfixture. For example, the LED packages 200, 300 and/or 400 could be usedin place of the LED packages 142A, 142B that are included in the solidstate light fixture 100 that is discussed above with reference to FIGS.11A-11C.

FIGS. 16A-16C illustrate a solid state light bulb 600 according to stillfurther embodiments of the present invention. In particular, FIG. 16A isa perspective view of the solid state light bulb 600, FIG. 16B is across-sectional view of the solid state light bulb 600, FIG. 16C is aplan view of a submount of the solid state light bulb 600 that has aplurality of LED packages mounted thereon. FIG. 16D is a perspectiveview of a modified version of the solid state light bulb 600 thatincludes a secondary optical structure according to some otherembodiments.

As shown in FIGS. 16A-16D, the solid state light bulb 600 comprises abody 610, a secondary optical structure 620, a dome 630 and a submount640 with a plurality of LED packages 642 mounted thereon. The body 610and the dome 630 may be any conventional body and dome, respectively,and hence these elements will not be discussed further herein. In thedepicted embodiment, the body includes a heat sink 612, but it will beappreciated that this heat sink 612 may be omitted in other embodiments.The submount 640 may be similar to the submount 120 discussed above withrespect to FIG. 11B. However, the layout of the LED packages 642 on thesubmount 640 differs from the layout of the LED packages 142 on thesubmount 120 of FIG. 11B. In particular, on submount 640, seven of theLED packages 642 are clustered in the center of the submount 640, andthe other seven LED packages 642 are dispersed around the periphery ofthe submount 640 to define a circle. It will also be noted that each LEDpackage 642 comprises a multi-zone emitter in which light having twodistinct colors is output from an individual LED package 642. The LEDpackages 642 may be formed, for example, according to the discussion ofFIGS. 12A-12B above.

The secondary optical structure 620 is mounted within the dome 630 abovethe submount 640. The secondary optical structure 620 may comprise, forexample, a total internal reflection optical structure, two versions ofwhich are schematically shown in FIGS. 16B and 16D. A total internalreflection optical structure may comprise a highly efficient opticalstructure that receives light and reflects the light so that it isemitted from the structure in a different, desired direction. For lightbulbs, it is often desirable to have much of the light emit from theside of the dome 630 or even to shine downwardly below the body 610 ofthe light bulb 600. The total internal reflection optical structure 620may redirect at least a portion of the upwardly directed light emittedby the LED packages 642 so that it is emitted at various angles throughthe side of the dome 630.

Referring to FIGS. 16B-D, seven of the LED packages 642 are directlyunderneath the total internal reflection optical structure 620 (thelocation of the total internal reflection optical structure 620 is shownby the circle drawn in a dashed line in FIG. 16C) and hence most of thelight output by these LED packages 642 will be redirected by the totalinternal reflection optical structure 620. The remaining LED packages642 are positioned below and around the periphery of the total internalreflection optical structure 620. Some of the light emitted by these LEDpackages 642 may be reflected off the sides of the total internalreflection optical structure 620 and/or captured by the total internalreflection optical structure 620 and redirected, while other of thelight emitted by these LED packages 642 may exit the light bulb 600without interacting with the total internal reflection optical structure620.

While the solid state light fixtures according to embodiments of thepresent invention that are discussed above are implemented using, forexample, blue-shifted-yellow/green and blue-shifted-red LED packages, itwill be appreciated that in other embodiments violet or ultraviolet LEDscould be used in place of the blue LEDs. Thus, it will be appreciatedthat all of the above-described embodiments could be implemented usingblue, violet and/or ultraviolet LEDs, and hence the change in the outputof the LEDs as a function of operating temperature and/or as a functionof hours of operation (lifetime) may be similar, reducing or eliminatingany need for control circuitry that modifies the drive currents suppliedto the LEDs based on operating temperature, lifetime or measured outputof the LEDs (as the luminous flux and color of the light. Herein, theterm “UV/blue-shifted-yellow/green LED packages” refers to an LEDpackage having one or more LEDs that emit light in the ultraviolet,violet or blue color ranges that have an associated recipientluminophoric medium that includes phosphor(s) that receive theultraviolet/violet/blue light emitted by the LED(s) and in responsethereto emit light having a peak wavelength in the yellow or green colorranges.

As described above, pursuant to some embodiments of the presentinvention, solid state light fixtures are provided that include aplurality of blue-shifted-yellow/green LED packages and a plurality ofblue-shifted-red LED packages. These solid state light fixture may emitlight having a correlated color temperature of between 1800 K and 5500K, a CRI value of between 80 and 99, a CRI R9 value of between 15 and75, and a Qg value of between 90 and 110 when theblue-shifted-yellow/green LED packages and the blue-shifted-red LEDpackages are operating at steady-state operating temperatures of atleast 80° C.

In some embodiments, each blue-shifted-yellow/green LED package maycomprise a first blue LED and an associated first recipient luminophoricmedium that includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and each blue-shifted-red LED package may comprise a secondblue LED and an associated second recipient luminophoric medium thatincludes a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In some suchembodiments the first blue LEDs may have a first average peak wavelengththat is less than a second average peak wavelength of the second blueLEDs. For example, the first blue LEDs may each have a peak wavelengththat is less than 455 nm and the second blue LEDs may each have a peakwavelength that is more than 460 nm.

In some embodiments, the first recipient luminophoric mediums mayinclude both the Y₃Al₅O₁₂:Ce phosphor and the Lu₃Al₅O₁₂:Ce phosphor andno red phosphor. Likewise, in some embodiments, two different types ofblue-shifted-red LED packages may be provided, where the each differenttype includes a different (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In otherembodiments, each blue-shifted-red LED package may include two different(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors that are mixed together in thesame recipient luminophoric medium. In each case, the peak wavelength ofthe two different (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphors may bedifferent. For example, the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphormay have a peak wavelength between 615 and 624 nm and the second(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor may have a peak wavelength between625 nm and 640 nm.

In some embodiments, the solid state light fixture may be an A-serieslight bulb such as an A19 or A21 light bulb. The solid state lightfixture may also be a candelabra light bulb. Theblue-shifted-yellow/green LED packages and the blue-shifted-red LEDpackages may be surface mounted on a printed circuit board in someembodiments such that each of the blue-shifted-yellow/green LED packagesis immediately adjacent a respective one of the blue-shifted-red LEDpackages.

In some embodiments, a first of the blue-shifted-yellow/green LEDpackages and a first of the blue-shifted-red LED packages may beimplemented together as a packaged LED component that includes at leastone LED on a submount and a first recipient luminophoric medium thatonly includes yellow and/or green phosphors on a first side of thesubmount and a second recipient luminophoric medium that only includesred phosphors on a second side of the submount that is opposite thefirst side.

Pursuant to further embodiments of the present invention, packaged LEDcomponents are provided that include a submount having an LED mountingsurface; at least one LED on the LED mounting surface; and a firstrecipient luminophoric medium having a first phosphor on top of a firstregion of the LED mounting surface and a second recipient luminophoricmedium having a second phosphor that is different from the firstphosphor and that emits light having a peak wavelength in the red colorrange on top of the second region of the LED mounting surface. In theseembodiments, the first recipient luminophoric medium is separate fromthe second recipient luminophoric medium and the second recipientluminophoric medium is not on top of the first region and the firstrecipient luminophoric medium is not on top of the second region.

In some embodiments, these packaged LED components may include a dividerthat extends across the LED mounting surface to define the first regionand the second region. The LED mounting surface may be within a cavity,and the divider may divide the cavity into first and secondsub-cavities. In such embodiments, the first recipient luminophoricmedium may be in the first sub-cavity and the second recipientluminophoric medium may be in the second sub-cavity. The distancebetween the first sub-cavity and the second sub-cavity is less than twocentimeters in some embodiments. In some embodiments, the submount mayinclude a molded structure that defines the cavity and the first andsecond sub-cavities. In other embodiments, the divider may be a separatestructure from the material that defines the cavity. The divider maycomprise, for example, a reflective plastic material.

In some embodiments, the first recipient luminophoric medium may includea Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor and may emit lighthaving a peak wavelength in the green or yellow color range, and thesecond recipient luminophoric medium may include at least a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

Pursuant to further embodiments of the present invention, solid statelight fixtures are provided that include a plurality ofblue-shifted-yellow/green LED packages and a plurality ofblue-shifted-red LED packages, where the light emitted by the solidstate light fixture has an emission spectrum having a first peak in theblue color range, a second peak between 525 nm and 575 nm, and a thirdpeak between 610 nm and 650 nm, and the third peak is larger than thefirst peak and the second peak. The second peak may be a shoulder formedon a side of the third peak. The second peak may be between 535 nm and555 nm, and the third peak may be between 615 nm and 630 nm.

In such embodiments, each blue-shifted-yellow/green LED package maycomprise a first blue LED and an associated first recipient luminophoricmedium that includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and each blue-shifted-red LED package comprises a second blueLED and an associated second recipient luminophoric medium that includesa first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor (and in some cases, asecond (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that emits light having apeak wavelength that is higher than the peak wavelength of the lightemitted by the first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor as well). Thesolid state light fixture may emit light having a correlated colortemperature of between 1800 K and 5500 K, a CRI value between 80 and 99,a CRI R9 between 15 and 75, and a Qg value between 90 and 110 when LEDsin the blue-shifted-yellow/green LED packages and the LEDs in theblue-shifted-red LED packages are operating at steady-state operatingtemperatures of at least 80° C.

Pursuant to still other embodiments of the present invention, lightingapparatus are provided that comprise a three dimensional shapedoptically transmissive enclosure such as the dome 130 described abovethat has an interior volume; a plurality of distinct yellow/green lightemitting regions within the interior volume, the yellow/green lightemitting regions comprising at least one gallium nitride based LED thatproduces shorter wavelength light and at least one first recipientluminophoric medium that downconverts at least some of the shorterwavelength light to longer wavelength light; and a plurality of distinctred/orange light emitting regions within the interior volume, thered/orange light emitting regions comprising at least one galliumnitride based LED that produces shorter wavelength light and at leastone second recipient luminophoric medium that downconverts at least someof the shorter wavelength light to longer wavelength light. The lightingapparatus emits white light from the optically transmissive enclosurehaving a correlated color temperature between 1800 K and 5500 K and aCRI value of greater than 80. The light emitted by the lightingapparatus may have a CRI R9 value between 15 and 75, and a Qg valuebetween 90 and 110 when the gallium nitride based LEDs are operating atsteady-state operating temperatures of at least 80° C. in someembodiments. The lighting apparatus may be, for example, an A serieslight bulb.

In some embodiments, the at least one first recipient luminophoricmedium may include a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and the at least one second recipient luminophoric medium mayinclude a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. The at least onesecond recipient luminophoric medium may further include a second(C_(a1-x)S_(rx))SiAlN₃:E^(u2+) phosphor that has a peak wavelength thatis greater than a peak wavelength of the first(C_(a1-x)S_(rx))SiAlN₃:E^(u2+) phosphor in some embodiments.

In other embodiments, the lighting apparatus may further include asecond plurality of distinct red/orange light emitting regions that arewithin the interior volume, the second red/orange light emitting regionscomprising at least one gallium nitride based LED that produces shorterwavelength light and at least one third recipient luminophoric mediumthat downconverts at least some of the shorter wavelength light tolonger wavelength light, wherein a peak wavelength of the light emittedby the at least one third recipient luminophoric medium exceeds a peakwavelength of the light emitted by the at least one second recipientluminophoric medium.

Pursuant to yet further embodiments of the present invention, lightingapparatus may be provided that comprise an optically transmissiveenclosure comprising an interior volume and shaped in accordance with anA series bulb; a plurality of distinct yellow/green light emittingregions that are configured to emit light into the interior volume, theyellow/green light emitting regions comprising at least one galliumnitride based LED that produces shorter wavelength light and at leastone first recipient luminophoric medium that downconverts at least someof the shorter wavelength light to longer wavelength light; and aplurality of distinct red/orange light emitting regions that areconfigured to emit light into the interior volume, the red/orange lightemitting regions comprising at least one gallium nitride based LED thatproduces shorter wavelength light and at least one second recipientluminophoric medium that downconverts at least some of the shorterwavelength light to longer wavelength light. The lighting apparatus mayemit light having a correlated color temperature of between 1800 K and5500 K, a CRI value between 80 and 99, a CRI R9 value between 15 and 75,and a Qg value between 90 and 110 when the gallium nitride based LEDsare operating at steady-state operating temperatures of at least 80° C.

In some embodiments, the at least one first recipient luminophoricmedium may include a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Cephosphor, and the at least one second recipient luminophoric medium mayinclude a first (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In some cases, theat least one second recipient luminophoric medium may also include asecond (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor that has a peak wavelengththat is greater than a peak wavelength of the first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor. In other embodiments, the lightingapparatus may further include a second plurality of distinct red/orangelight emitting regions that are configured to emit light into theinterior volume, the second red/orange light emitting regions comprisingat least one gallium nitride based LED that produces shorter wavelengthlight and at least one third recipient luminophoric medium thatdownconverts at least some of the shorter wavelength light to longerwavelength light, wherein a peak wavelength of the light emitted by theat least one third recipient luminophoric medium exceeds a peakwavelength of the light emitted by the at least one second recipientluminophoric medium.

According to still other embodiments of the present invention, A-seriessolid state light bulbs are provided that include an A-series light bulbbody; a diffuse optical enclosure mounted on the A-series light bulbbody; a reflector within the diffuse optical enclosure; and a submounthaving at least one blue-shifted-yellow/green emitter and at least oneblue-shifted-red emitter in a central section of the submount and aplurality of blue-shifted-yellow/green emitters and a plurality ofblue-shifted-red emitters arranged around a periphery of the submount.In these light bulbs, each blue-shifted-yellow/green emitter emits lighthaving a peak wavelength in the yellow or green color ranges and eachblue-shifted-red emitter emits light having a peak wavelength in the redcolor range. The reflector may be positioned above the submount and mayhave a truncated frusto-conical shape in some embodiments.

In some embodiments, the at least one blue-shifted-yellow/green emitterand at least one blue-shifted-red emitter that are in the centralsection of the submount comprise a packaged LED component that includesat least one blue light emitting diode (“LED”) on an LED mountingsurface, a first recipient luminophoric medium having a first phosphoron top of a first region of the LED mounting surface and a secondrecipient luminophoric medium having a second phosphor that is differentfrom the first phosphor on top of a second region of the LED mountingsurface, wherein the first recipient luminophoric medium is separatefrom the second recipient luminophoric medium and the second recipientluminophoric medium is not on top of the first region and the firstrecipient luminophoric medium is not on top of the second region. Thesolid state light fixture may be an A19 or A21 solid state light bulb.In some embodiments, the first and second recipient luminophoric regionsmay be disposed side-by-side on the at least one LED.

Pursuant to still other embodiments of the present invention, solidstate light fixtures are provided that include a diffuse opticalenclosure having an interior volume; a plurality ofblue-shifted-yellow/green emitters that are configured to emit lightinto the interior volume; a plurality of blue-shifted-red emitters thatare configured to emit light into the interior volume; and a controllerthat controls the relative current levels provided to the plurality ofblue-shifted-yellow/green emitters and the plurality of blue-shifted-redemitters. This controller is configured to increase the relative amountof drive current supplied to the blue-shifted-red emitters as comparedto the blue-shifted-yellow/green emitters when the solid state lightfixture is dimmed.

In some embodiments, first light emitted from the diffuse opticalenclosure may comprise white light having a correlated color temperatureof between 1800 K and 5500 K when the solid state light fixture is notdimmed, and second light emitted from the diffuse optical enclosure whenthe solid state light fixture is dimmed by at least 40% becomesnon-white light with an increased red component.

In some embodiment, each blue-shifted-yellow/green emitter may comprisea first blue LED and an associated first recipient luminophoric mediumthat includes a Y₃Al₅O₁₂:Ce phosphor and/or a Lu₃Al₅O₁₂:Ce phosphor, andeach blue-shifted-red emitter comprises a second blue LED and anassociated second recipient luminophoric medium that includes a first(Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor.

The above-described solid state light fixtures according to embodimentsof the present invention may exhibit high luminous flux, high qualitycolor rendering, a good ability to accurately reproduce red colors, andoverall high color quality and vividness, and may maintain suchperformance even at high operating temperatures (e.g., temperatures of100° C.).

While embodiments of the present invention have primarily been discussedabove with respect to solid state light bulbs, and may have particularutility with respect to various small form factor light fixtures as wellas light fixtures having three dimensional optically transmissiveenclosures, it will be appreciated that the same techniques may be usedin other types of solid state light fixtures. For example, each of theembodiments disclosed herein may be alternatively implemented in othertypes of solid state light fixtures including, for example, downlights,troffers, streetlights, canopy lights, parking garage lights, lightsthat use a two dimensional planar optically transmissive lens, such as adiffuse lens and other lighting fixtures.

As a simple example of other light fixtures that may use theblue-shifted-yellow/green LED packages and blue-shifted-red LED packagesin the manner described above, FIG. 15A illustrates a PAR-seriesdownlight 500. The PAR-series downlight 500 may includeblue-shifted-yellow/green LED packages 502 and blue-shifted-red LEDpackages 504 on a submount 506 according to any of the above-describedembodiments of the present invention. The PAR-series downlight 500 mayinclude, for example, the submount printed circuit board 140 of FIG. 11Bhaving the LED packages 142 mounted thereon. Theblue-shifted-yellow/green LED packages and blue-shifted-red LED packagesaccording to any of the above-described embodiments of the presentinvention may also be implemented in various other downlights, such as,for example, in PAR and BR series downlights disclosed in U.S. Pat. Nos.8,591,062 and 8,596,819 and U.S. patent application Ser. No. 14/306,342,each of which are incorporated herein by reference. As another example,FIG. 15B illustrates a troffer light fixture 510. The troffer lightfixture 510 may include blue-shifted-yellow/green LED packages 512 andblue-shifted-red LED packages 514 according to any of theabove-described embodiments of the present invention. Theabove-described blue-shifted-yellow/green LED packages andblue-shifted-red LED packages according to embodiments of the presentinvention may also be implemented in various other lighting fixtures,such as, for example, in the waveguide-based troffers disclosed in U.S.Patent Publication No. 2014/0347885, in the troffer style fixturesdisclosed in U.S. Patent Publication No. 2012/0051041 and/or in thewaveguide based garage lights disclosed in U.S. Patent Publication No.2014/0355302, each of which are incorporated herein by reference. Inanother example, FIG. 15C illustrates a solid state streetlight 520according to further embodiments of the present invention. Thestreetlight 520 may be implemented according to any of theabove-described embodiments of the present invention. Other streetlightsand outdoor lighting fixtures that can be implemented using theabove-described blue-shifted-yellow/green LED packages andblue-shifted-red LED packages according to embodiments of the presentinvention include the streetlights disclosed in U.S. U.S. Pat. No.8,622,584; U.S. Pat. No. 8,425,071; U.S. Pat. No. 9,028,087; and U.S.Patent Publication No. 2015/0253488, each of which are incorporatedherein by reference. Finally, FIG. 15D illustrates a solid statedownlight 530 according to some embodiments of the present invention.The a solid state downlight 530 may include blue-shifted-yellow/greenLED packages and blue-shifted-red LED packages according to any of theabove-described embodiments of the present invention. Other downlightsand similar fixtures that can be implemented using the above-describedblue-shifted-yellow/green LED packages and blue-shifted-red LED packagesaccording to embodiments of the present invention include the downlightsdisclosed in U.S. Pat. No. 8,622,584; U.S. Pat. No. 8,425,071; U.S. Pat.No. 9,028,087; U.S. Pat. No. 8,882,311; and U.S. Patent Publication No.2015/0253488, each of which are incorporated herein by reference. In allembodiments, the light can be maintained constant over time and/or as afunction of temperature through feedback control, open or closed loopcontrol or, alternatively, may be allowed to simply degrade with timewithout significant shift in color point.

FIGS. 17A-17C illustrate a troffer light fixture 700 according tofurther embodiments of the present invention. In particular, FIG. 17A isa perspective view of the troffer light fixture 700, FIG. 17B is a planview of the troffer light fixture 700 and FIG. 17C is a perspective viewof the LED package mounting structure and the LED packages 740, 750included in the troffer light fixture 700.

As shown in FIG. 17A, the troffer light fixture 700 includes a backplate710 and a dome 720. The dome 720 may or may not also function as adiffuser that mixes light emitted by the LED packages 740, 750. As shownin FIG. 17B, a printed circuit board 730 or other LED package mountingstructure may be mounted on the backplate 710 underneath the dome 720.

Turning now to FIG. 17C, a plurality of blue-shifted-yellow/green LEDpackages 740 and a plurality of blue-shifted-red LED packages 750 aremounted in rows on the package mounting surface 730. Theblue-shifted-yellow/green LED packages 740 may be any of theblue-shifted-yellow/green LED packages according to embodiments of thepresent invention disclosed herein, and the blue-shifted-red LEDpackages 750 may be any of the blue-shifted-red LED packages accordingto embodiments of the present invention disclosed herein. In someembodiments, a first subset of the blue-shifted-red LED packages 750 mayinclude a first red phosphor that has a first peak wavelength and asecond subset of the blue-shifted-red LED packages 750 may have a secondred phosphor that has a second peak wavelength that is longer than thefirst peak wavelength. The first subset of the blue-shifted-red LEDpackages 750 that have the first red phosphor having the shorter peakwavelength may be brighter than the second subset of theblue-shifted-red LED packages 750 that have the second red phosphor.Inclusion of the second subset of the blue-shifted-red LED packages 750that have the second red phosphor may help improve the CRI and/or theCRI R9 performance of the light fixture 700. In other embodiments, eachblue-shifted-red LED package 750 may have both the first and second redphosphors mixed together therein in order to allow all of theblue-shifted-red LED packages 750 to be the same component. In stillother embodiments, each blue-shifted-red LED package 750 may onlyinclude one phosphor and all of the blue-shifted-red LED packages 750may be the same. Other variations are possible.

The blue-shifted-yellow/green LED packages 740 may, for example, includea YAG:Ce phosphor, a LuAG:Ce phosphor or a combination thereof. In someembodiments some of the blue-shifted-yellow/green LED packages 740 maybe blue-shifted-yellow LED packages that include a YAG:Ce phosphor whileothers of the blue-shifted-yellow/green LED packages 740 may beblue-shifted-green LED packages that include a LuAG:Ce phosphor. Instill other embodiments, each blue-shifted-yellow/green LED package 740may include the same type(s) of phosphor(s), but some of theblue-shifted-yellow/green LED packages 740 may include different amountsof the phosphor(s) than others of the blue-shifted-yellow/green LEDpackages 740.

As shown in FIG. 17C, there need not be a one-to-one correspondencebetween the number of blue-shifted-yellow/green LED packages 740 and thenumber of blue-shifted-red LED packages 750. In the pictured embodiment,six groups of eleven (11) blue-shifted-yellow/green LED packages 740 andnine (9) blue-shifted-red LED packages 750 are provided for a total of120 LED packages 740, 750. Because there are moreblue-shifted-yellow/green LED packages 740 than blue-shifted-red LEDpackages 750, in some locations two blue-shifted-yellow/green LEDpackages 740 may be directly adjacent each other.

TABLE 5 illustrates measured data for a conventional troffer lightfixture that uses LED packages where the yellow/green and red phosphorsare mixed together in each LED package as compared to the light fixture700 that has separate blue-shifted-yellow/green and blue-shifted-red LEDpackages 740, 750. As shown in TABLE 5, the light fixture 700 accordingto embodiments of the present invention provides a higher lumen outputand improved lumens/watt performance (nearly 10% higher in each case)while providing essentially identical color rendering performance. FIG.17D illustrates the emission spectra of the two above-discussed trofferlight fixtures. The higher luminous output for light fixture 700 resultsfrom the increased emission in regions near the center of the eyeresponse curve of FIG. 3.

TABLE 5 Device CCT (K) LPW Lumens CRI R9 Conventional Light Fixture 3420109.2 3937 90.8 60.1 Light Fixture 700 3398 119.0 4306 90.9 59.0

Pursuant to further embodiments of the present invention, light fixtureshaving adjustable or “tunable” correlated color temperatures areprovided. In some embodiments, these light fixtures may include at leastthree separately controllable strings of LED packages (referred toherein as “LED strings”) and at least three different types of LEDpackages. The correlated color temperature of the light emitted by theselight fixtures may be adjusted by adjusting the relative amounts ofcurrent supplied to each of the three strings of LED packages. Anexample embodiment of such a light fixture will now be described withreference to FIGS. 18A-18F.

In particular, FIG. 18A is a perspective view of a tunable troffer lightfixture 800 according to further embodiments of the present invention.FIG. 18B is an enlarged view of a portion of a printed circuit board ofthe tunable troffer light fixture 800 that acts as the LED packagemounting structure. FIG. 18C is an enlarged portion of the 1931 CIEChromaticity Diagram that illustrates a range of color points that maybe achieved using the tunable troffer light fixture 800, including colorpoints within the E3-E7 color bins. FIG. 18D is a graph illustrating theintensity of the radiation emitted as a function of wavelength for eachof the different types of LED packages included in the tunable trofferlight fixture 800. FIG. 18E is a graph illustrating the intensity of theradiation emitted as a function of wavelength for the tunable trofferlight fixture 800 when operated to fall within each of the E3 through E7regions of FIG. 18C. FIG. 18F illustrates two example connection schemesfor the different types of LED packages included in the tunable trofferlight fixture 800.

Referring to FIGS. 18A-18B, the troffer light fixture 800 includes abackplate 810 and an LED package mounting structure 830 which is in theform of a printed circuit board. The troffer light fixture 800 mayfurther include a dome (not shown) such as the dome 720 of troffer lightfixture 700. The printed circuit board 830 may be mounted on thebackplate 810 behind the diffuser. A plurality ofblue-shifted-yellow/green LED packages 840 and a plurality ofblue-shifted-red LED packages 850 are mounted in three rows on theprinted circuit board 830. The blue-shifted-yellow/green LED packages840 may be any of the blue-shifted-yellow/green LED packages accordingto embodiments of the present invention disclosed herein, and theblue-shifted-red LED packages 850 may be any of the blue-shifted-red LEDpackages according to embodiments of the present invention disclosedherein.

As shown in FIG. 18B, the blue-shifted-yellow/green LED packages 840 andthe blue-shifted red LED packages 850 may be arranged in three generallyparallel, spaced-apart rows 860, 862, 864. The blue-shifted-yellow/greenLED packages 840 may be in the two outside rows 862, 864, and theblue-shifted-red LED packages 850 may be in the middle row 860 that isbetween the two outside rows 862, 864. In some embodiments, the LEDpackages 840 in the second row 862 may compriseblue-shifted-yellow/green LED packages 840A and the LED packages 840 inthe third row 864 may comprise blue-shifted-yellow/green LED packages840B, where the blue-shifted-yellow/green LED packages 840A are designedto emit different color light than the blue-shifted-yellow/green LEDpackages 840B, as will be explained in greater detail below.

In one example embodiment, the troffer light fixture 800 includes 180LED packages (i.e., 60 LED packages per row). The LED packages 840A,840B, 850 may be electrically connected in a plurality of LED strings.In an example embodiment, each of the three rows 860, 862, 864 mayinclude five strings of twelve adjacent LED packages each, with the LEDpackages in each string electrically connected, for example, in series.In this embodiment, five strings of LED packages 840A, five strings ofLED packages 840B, and five strings of LED packages 850 are included inthe light fixture 800.

In some embodiments, the LED packages 840A in the second row 862 mayinclude the same phosphor as the LED packages 840B in the third row 864,but may have a different amount of phosphor. In particular, the LEDpackages 840A may have a higher amount of phosphor than the LED packages840B. As a result, the LED packages 840A and 840B will emit light havingdifferent color points. The color point of the light emitted by thetroffer light fixture 800 may be changed by varying the currentsprovided to the respective different types of LED packages 840A, 840B,850. In some embodiments, the phosphor included in the LED packages840A, 840B may be a LuAG:Ce phosphor. In other embodiments, the phosphorincluded in the LED packages 840A, 840B may be a YAG:Ce phosphor. Instill other embodiments, the phosphor included in the LED packages 840A,840B may be a combination of YAG:Ce phosphor and a LuAG:Ce phosphor.Other phosphors may also be used. In some embodiments, each LED package840A may include a single type of phosphor (e.g., a LuAG:Ce phosphor),and the LED packages 840A may have at least two times more of thisphosphor than the LED packages 840B. In other embodiments, each LEDpackage 840A may include a single type of phosphor (e.g., a LuAG:Cephosphor), and the LED packages 840A may have at least three times moreof this phosphor than the LED packages 840B. In still other embodiments,each LED package 840A may include a single type of phosphor (e.g., aLuAG:Ce phosphor), and the LED packages 840A may have at least four,five, six or even seven times more of this phosphor than the LEDpackages 840B. The LED packages 840A may be referred to herein as “highphosphor LED packages as they may include a greater amount of phosphorthan the “low phosphor LED packages 840B.

The red phosphor included in the blue-shifted-red LED packages 850 maybe a (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor in some embodiments. The ratioof the amount of yellow/green phosphor (e.g., LuAG:Ce) included in thehigh phosphor blue-shifted-yellow/green LED packages 840A to the amountof red phosphor (Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor) included in theblue-shifted-red LED packages 850 may be between about 2 and 7 in someembodiments (i.e., the amount of LuAG:Ce phosphor may exceed the amountof ((Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor by between a factor of 2 and afactor of 7). In other embodiments, this ratio may be between 3 and 6.In still other embodiments, this ratio may be between 3 and 5.

The ratio of the amount of yellow/green phosphor (e.g., LuAG:Ce)included in the low phosphor blue-shifted-yellow/green LED packages 840Bto the amount of red phosphor ((Ca_(1-x)Sr_(x))SiAlN₃:Eu²⁺ phosphor)included in the blue-shifted-red LED packages 850 may be between about0.3 and 2 in some embodiments. In other embodiments, this ratio may bebetween 0.5 and 1.5. In still other embodiments, this ratio may bebetween 0.6 and 1.0.

Using the same type of phosphor in the LED packages 840A and 840B, butin different amounts, may be advantageous for several reasons. First, byusing the same phosphor any change in the performance of the phosphorover time and/or with temperature will tend to be the same for the LEDpackages 840A and 840B. This may lessen the impact of such changes onthe light output by the light fixture 800. Additionally, using the sametype of phosphor may simplify the manufacturing process.

FIG. 18C is an enlarged portion of the 1931 CIE Chromaticity Diagramthat illustrates a range of color points that may be achieved using thetunable troffer light fixture 800. As shown in FIG. 18C, in someembodiments, the color point 871 of the light emitted by theblue-shifted-red LED packages 850 may be selected to form a tie line 881with the color point 872 of the blue-shifted-yellow/green LED packages840A that runs through the E7 bin on the 1931 CIE Chromaticity Diagram.This may be seen graphically in FIG. 18C, where the tie line 881 thatconnects the color point 871 for the LED packages 850 to the color point872 for the LED packages 840A runs through the E7 color bin. Likewise,the color point 873 of the light emitted by theblue-shifted-yellow/green LED packages 840B may be selected to form atie line 885 with the color point 871 of the LED packages 850 that runsthrough the E3 bin on the 1931 CIE Chromaticity Diagram. Additional tielines 882-884 are illustrated in FIG. 18C which extend from the colorpoint 871 for the LED packages 850 to points on a line 886 that extendsbetween color points 872 and 873. The tie lines 882-884 extend throughthe E4, E5 and E6 color bins on the 1931 CIE Chromaticity Diagram,respectively. Thus, it can be seen that by varying the relative levelsof the currents supplied to the three rows of LED packages 860, 862, 864the troffer light fixture 800 may be configured to emit light having acolor point in any of the E3 through E7 color bins. In principle, anycolor point that is within the triangle formed by the three anchorpoints can be reached with a given combination of currents for the threestrings of LED packages—although points on the black body locus are ofprincipal interest for applications.

TABLE 6 illustrates measured performance data for the troffer lightfixture 800 when configured to operate at respective color points ineach of the E3-E7 color bins. In TABLE 6, references to LoP Y/G refer tothe LED packages 840B that have the lower amount of phosphor, referencesto HiP Y/G refer to the LED packages 840A that have the higher amount ofphosphor, and references to R refer to the LED packages 850. As shown inTABLE 6, the troffer light fixture 800 according to embodiments of thepresent invention exhibits high lumens/watt performance while providingexcellent color rendering performance when operated in all five colorbins E3-E7.

TABLE 6 LoP Y/G HiP Y/G R Color Current Current Current CCT Point (mA)(mA) (mA) LPW (K) CRI R9 E3 85 0 43 172.4 4974 90.6 37.2 E4 54 20 55175.8 4111 92.4 42.5 E5 34 34 61 175.8 3707 92.2 39.5 E6 15 47 68 171.63329 92.4 37.6 E7 0 58 75 166.0 3063 91.1 30.7

FIG. 18D is a graph illustrating the intensity of the radiation emittedas a function of wavelength for each of the different types of LEDpackages included in the tunable troffer light fixture 800. As shown inFIG. 18D, the LED packages 840A and 840B have similar emission spectra,as they use the same phosphor, but the lower phosphor LED packages 840Bhave a large amount of pass-through blue light and relatively lessgreen/yellow emission, while the high phosphor LED packages 840A absorbmost of the blue light resulting in only a small amount of blue emissionand a larger green/yellow emission.

FIG. 18E is a graph illustrating the intensity of the radiation emittedas a function of wavelength for the tunable troffer light fixture 800when operated to fall within each of the E3 through E7 regions or “colorbins” of FIG. 18C. As can be seen in FIG. 18E, the general shape of eachemission spectrum is similar, but the relative intensities of each peakvary. In particular, the emission spectra for the higher colortemperature samples (e.g., E3, E4) have higher emission intensities inthe blue color range and lower emission intensities in the green, yellowand red color ranges. Conversely, the emission spectra for the lowercolor temperature samples (e.g., E7, E6) have lower emission intensitiesin the blue color range and higher emission intensities in the green,yellow and red color ranges.

Referring again to FIG. 18B, in some embodiments, the first throughthird rows 860, 862, 864 of LED packages may comprise a first middle row860 of LED packages 850, a second outside row 862 of LED packages 840A,and a third outside row 864 of LED packages 840B. The first row 860 ofLED packages 850 is between the second and third rows 862, 864. Thethree rows 860, 862, 864 may be spaced apart and generally parallel toeach other. The LED packages 840A, 840B, 850 may also be aligned incolumns of three LED packages each as shown, although they need not bein some embodiments. As shown in TABLE 6 above, in order to operate thetunable troffer light fixture 800 in the E3 color bin (CCT of about 5000K), a relatively high current may be provided to the LED string(s) inthe third row 864 (i.e., to the low phosphor LED packages 840B) whilelittle or no current is supplied to the LED strings in the second row862 (i.e., to the high phosphor LED packages 840A), and relatively lesscurrent is supplied to the LED packages 850 included in the first(middle) row 860. As is also shown in TABLE 6, in order to operate thetunable troffer light fixture 800 in the E7 color bin (CCT of about 3000K), a relatively high current may be provided to the LED string(s) inthe second row 862 (i.e., to the high phosphor LED packages 840A) whilelittle or no current is supplied to the LED strings in the third row 864(i.e., to the low phosphor LED packages 840B), and relatively morecurrent is supplied to the LED packages 850 included in the first(middle) row 860. TABLE 6 likewise shows the relative currents suppliedto the LED packages 840A, 840B, 850 in order to operate the lightfixture 800 in the E4-E6 color bins.

FIG. 18F is a schematic diagram illustrating the layout arrangement andelectrical connections for the LED packages 840A, 840B and 850 accordingto two example embodiments of the present invention. As shown in the tophalf of FIG. 18F, in the first example embodiment, the blue-shifted redLED packages 850 are all positioned in the first row 860, the highphosphor blue-shifted-yellow/green LED packages 840A are all positionedin the second row 862 which is on a first side of the first row 860, andthe low phosphor blue-shifted-yellow/green LED packages 840B are allpositioned in the third row 864 which is on a second side of the firstrow 860 that is opposite the first side. This layout is consistent withthe layout shown in FIG. 18B. A total of sixty LED packages 840A, 840Bor 850 are included in each row. These sixty LED packages are dividedinto five strings of twelve LED packages each, with the LED packagesbeing electrically connected in series. Circuit traces 832 on theprinted circuit board 830 may be used to make these series electricalconnections. Each LED string may be connected to a power supply (notshown).

As is shown in the bottom half of FIG. 18F, in an alternativeembodiment, the circuit board 830 (or other LED package mountingsurface) may have circuit traces 832A, 832B, 832C (collectively 832) onat least two different levels which may allow electrically connectingLED packages 840A, 840B, 850 that are in different ones of the rows 860,862, 864. In one example embodiment using this technique, the LEDpackages in rows 862 and 864 may each alternate between LED packages840A and 840B. In the depicted embodiment, the LED packages 840A areelectrically connected in series and the LED packages 840B areelectrically connected in series. Accordingly, the circuit traces 832Aconnecting the LED packages 840A criss-cross with the circuit traces832B connecting the LED packages 840B. As a result, both the circuittraces 832A and the circuit traces 832B cross the circuit traces 832C inmany locations. In the depicted embodiment the LED packages 840A and840B are aligned in columns (of two LED packages each) while the LEDpackages 850 are offset from the LED packages 840A and 840B in thecolumn direction. It will be appreciated, however, that otherarrangements are possible.

One potential advantage of the LED package layout shown in the bottomportion of FIG. 18F is that when the LED packages 840A are all alignedin the row 862 and the LED packages 840B are all aligned in the row 864,color separation may appear as the light fixture 800 is tuned to operatein the E3 or E7 color bins, as the contribution of either row 862 or 864becomes low or non-existent under such operating conditions. Forexample, as shown in TABLE 6, when the troffer light fixture 800 isoperated in the E7 color bin, the current supplied to the low phosphorblue-shifted-yellow/green LED packages 840B is approximately zero. Assuch, if the LED packages 840B are all aligned in a single row 864 onthe second side of the row 860 of red LED packages 850, then the red LEDpackages 850 will effectively be located in an “outside” row when thelight fixture 800 is operated under these conditions.

Unfortunately, the human eye may be very perceptive to the color red,and when the LED packages 800 are positioned in the arrangement shown inthe top half of FIG. 18F, a human observer looking at the light fixture800 may see a row of generally greenish light next to a row of generallyreddish light when the light fixture 800 is operated in the E7 colorbin, especially under dimming operation. This same effect may occur whenthe light fixture 800 is operated in the E3 color bin. By including bothLED packages 840A and 840B in each of the two outside rows 862, 864 thistendency for color separation to appear when the light fixture 800 isoperated at either end of its tunable operating range may be reduced oreliminated, as at least half of the LED packages in both rows 862 and864 will emit light under all of the operating conditions for the lightfixture 800.

It will also be appreciated that the layout arrangements of the LEDpackages of FIG. 18F may be modified in various ways. For example, asshown in FIG. 19A, the blue-shifted-yellow/green LED packages 840A, 840Bin the second and/or third rows 862, 864 need not be aligned in perfectrows. Likewise, as shown in FIG. 19B, the blue-shifted-red LED packages850 in the first row 860 need not be aligned in a perfect row. As shownin FIG. 19C, in further embodiments more than three rows of LED packagesmay be provided. In the particular embodiment shown in FIG. 19C, fiverows 860, 862, 864, 866, 868 of LED packages 840A, 840B, 842, 850 areprovided, including three different types of blue-shifted-yellow/greenLED packages 840A, 840B, 842 and blue-shifted-red LED packages 850. Aswill be discussed below, the use of more than two different types ofblue-shifted-yellow/green LED packages may be beneficial in certainsituations including, for example, applications where the light fixtureis to be tunable across a broad range of correlated color temperatures.In other embodiments, more than one type of blue-shifted-red LED package850 may be used. For example, the embodiments of FIG. 19A or 19B couldbe modified to include two central rows of blue-shifted-red LED packages850 that are arranged in a criss-cross configuration (like theblue-shifted-yellow/green LED packages 840A, 840B in FIG. 19A) or couldbe modified so that the single row of blue-shifted-red LED packages 850included two different types of blue-shifted-red LED packages 850.

Since the blue-shifted-yellow/green LED packages 840A, 840B may all bepart of the second and third LED string and the blue-shifted-red LEDpackages 850 may all be part of the first LED string, the light fixture800 to be configured to have increased red light contribution when thebulb is dimmed, which can be achieved by driving the blue-shifted-redLED packages 850 more heavily than the blue-shifted-yellow/green LEDpackages 840A, 840B when the light fixture 800 is dimmed. Such a dimmingfeature may be preferred as it mimics the dimming characteristics of aconventional incandescent light bulb which comparatively emits more redlight when dimmed. Thus, the correlated color temperature of the lightemitted from the light fixture may generally decrease with an increasinglevel of dimming. Thus, as the luminous flux of the light fixturedecreases, the correlated color temperature may also generally decrease.

Additionally, pursuant to embodiments of the present invention the LEDpackages 840A, 840B, 850 may be arranged on the printed circuit board830 or other LED package mounting surface so that theblue-shifted-yellow/green LED packages 840A, 840B generally surround theblue-shifted-red LED packages 850. This can be seen, for example, in theexample designs of FIGS. 19A-19C. As noted above, if one or more of theblue-shifted-red LED packages 850 are mounted along the outer rows 862,864, the color mixing may be insufficient to produce true white light,and hence an observer looking at the light fixture 800 may be able tosee the locations of the blue-shifted-red LED packages 850. While thisissue can be resolved by providing a diffusing mechanism such as adiffusing plate or dome, the use of such diffusing mechanisms reducesthe luminous output of the light fixture and increases the cost thereof,both of which are undesirable. The inventors have discovered that bylocating the blue-shifted-red LED packages 850 in one (or more) centerrows 860 with rows 862, 864 of blue-shifted-yellow/green LED packages840A, 840B on either side thereof, improved color mixing may beobtained.

Because of these color mixing issues, it may also be desirable to havethe rows 862, 864 of blue-shifted-yellow/green LED packages 840A, 840Bextend farther in each direction than the row 860 of blue-shifted-redLED packages 850. Examples of this configuration are once again shown inFIGS. 19A-19C. For example, in FIG. 19A the top row 862 ofblue-shifted-yellow/green LED packages 840A, 840B extends farther toboth the left and right than does the middle row 860 of blue-shifted-redLED packages 850. Similarly, the bottom row 864 ofblue-shifted-yellow/green LED packages 840A, 840B also extends fartherto both the left and right than does the middle row 860 ofblue-shifted-red LED packages 850. This arrangement may provide improvedcolor mixing. Since each row 860, 862, 864 may include the same numberof LED packages (e.g., 60), the blue-shifted-red LED packages 850 in themiddle row 860 may be spaced more closely together than theblue-shifted-yellow/green LED packages 840A, 840B that are included inthe outside rows 862, 864 to allow the rows of blue-shifted-yellow/greenLED packages 840A to extend farther in each direction than the row ofblue-shifted-red LED packages 850.

Thus, pursuant to some embodiments of the present invention, trofferlight fixtures may be provided that have a tunable color point. Thetroffer light fixture may include a plurality ofblue-shifted-yellow/green LED packages. The blue-shifted-yellow/greenLED packages may include both low-phosphor LED packages and highphosphor LED packages. The high phosphor LED packages have a higherphosphor conversion ratio than the low phosphor LED packages, meaningthat the phosphor included in each high phosphor LED package willconvert a higher percentage of the light emitted by the blue LEDincluded therein to light of a different wavelength as compared to thelow phosphor LED packages. A higher phosphor conversion ratio may beachieved, for example, by using two different phosphors that convertdifferent amounts of light per unit weight of phosphor and/or by usingdifferent amounts of phosphor in the two different LED package types.For example, in embodiments in which the low-phosphor LED packages andthe high phosphor LED packages include the same phosphor, the highphosphor LED packages will have a greater amount of the phosphor thanthe low phosphor LED packages. However, in other embodiments where thelow-phosphor LED packages and the high phosphor LED packages usedifferent types of yellow/green phosphors, this will not necessarily bethe case.

The troffer light fixture may also include a plurality ofblue-shifted-red LED packages. The blue-shifted-red LED packages mayextend in a first row. A first subset of the blue-shifted-yellow/greenLED packages may extend in a second row on a first side of theblue-shifted-red LED packages and a second subset of theblue-shifted-yellow/green LED packages may extend in a third row on asecond side of the blue-shifted-red LED packages. The two rows ofblue-shifted-yellow/green LED packages may be on opposed sides of therow of blue-shifted-red LED packages

In some embodiments, the blue-shifted-yellow/green LED packages in thesecond row may include both low phosphor LED packages and high phosphorLED packages and/or the blue-shifted-yellow/green LED packages in thethird row may include both low phosphor LED packages and high phosphorLED packages. The blue-shifted-red LED packages may be electricallyconnected in series to form a first LED string and the low phosphor LEDpackages may be electrically connected in series to form a second LEDstring. The second LED string may cross the first LED string. Forexample, in some embodiments, the second LED string may cross the firstLED string at least twice. In other embodiments, the second LED stringmay cross the first LED string in at least four locations. The highphosphor LED packages may be electrically connected in series to form athird LED string. The third LED string may cross the first LED string.For example, in some embodiments, the third LED string may cross thefirst LED string two, four or even more times. The third LED string mayalso cross the first LED string two, four or even more times. In someembodiments, the second and third strings of blue-shifted-yellow/greenLED packages may include X LED packages each, and the second string maycross the third string X−1 times. More than one first LED string, morethan one second LED string and/or more than one third LED string may beincluded in the light fixture.

A first end of the second row may extend beyond a first end of the firstrow, and a second end of the second row may extend beyond a second endof the first row. Likewise, a first end of the third row may extendbeyond the first end of the first row, and a second end of the third rowmay extend beyond the second end of the first row. In order to achievethis arrangement in embodiments that include the same number of lowphosphor blue-shifted-yellow/green LED packages, high phosphorblue-shifted-yellow/green LED packages and blue-shifted-red LEDpackages, an average separation between adjacent ones of theblue-shifted-red LED packages in the first row may be less than anaverage separation between adjacent ones of theblue-shifted-yellow/green LED packages in the second row and less thanan average separation between adjacent ones of theblue-shifted-yellow/green LED packages in the third row. Thisarrangement may ensure that the blue-shifted-red LED packages aresurrounded by the blue-shifted-yellow/green LED packages, which mayprovide for better color mixing.

In some embodiments, the low phosphor blue-shifted-yellow/green LEDpackages and the high phosphor blue-shifted-yellow/green LED packagesmay each include a single phosphor, and may include the same phosphor.In some embodiments, this phosphor may be a LuAG:Ce phosphor. The lowphosphor LED packages may each include a first amount of the phosphorand the high phosphor LED packages each include a second amount of thephosphor that is between, for example, two to seven times the firstamount.

Pursuant to other embodiments, tunable light emitting diode (LED) basedlight fixtures are provided that include a plurality of blue-shifted-redLED packages and a plurality of blue-shifted-yellow/green LED packages.The blue-shifted-yellow/green LED packages include both low-phosphor LEDpackages that each include a first amount of a first phosphor and highphosphor LED packages that each include a second amount of the firstphosphor. The first amount may be between twice and seven times thesecond amount in some embodiments.

The blue-shifted-red LED packages may extend in a first row and theblue-shifted-yellow/green LED packages may extend in both a second rowand in a third row, with the second row positioned on a first side ofthe first row and the third row positioned on a second side of the firstrow that is opposite the first side. The second and third rows may begenerally parallel to the first row. The second row may include both lowphosphor LED packages and high phosphor LED packages, and the third rowmay likewise include both low phosphor LED packages and high phosphorLED packages.

The blue-shifted-red LED packages may be electrically connected inseries to form a first LED string and the low phosphor LED packages maybe electrically connected in series to form a second LED string, and thesecond LED string may cross the first LED string in at least fourlocations. The high phosphor LED packages may be electrically connectedin series to form a third LED string. The first second and third LEDstrings may cross over other of the first through third LED stringsmultiple times (e.g., in at least two locations, in at least fourlocations, etc).

The second row may have respective endpoints that extend beyondrespective endpoints of the first row, and the third row may likewisehave respective endpoints that extend beyond respective endpoints of thefirst row. An average separation between adjacent ones of theblue-shifted-red LED packages in the first row may be less than anaverage separation between adjacent ones of theblue-shifted-yellow/green LED packages in the second row and/or lessthan an average separation between adjacent ones of theblue-shifted-yellow/green LED packages in the third row.

In some embodiments, the tunable troffer light fixture may be configuredto operate in any of the E3-E7 color bins, while providing a CRI of atleast 90 and a CRI R9 of at least 30 in each of the E3-E7 color bins. Insome embodiments, the light fixture may exhibit at least 130 lumens perwatt when operating under these conditions.

As shown in TABLE 6 above, in order to operate in the E3 color bin, thetunable troffer light fixture 800 reduces the current that is suppliedto the high phosphor blue-shifted-yellow/green LED packages 840A toessentially zero, while in order to operate in the E7 color bin, thetunable troffer light fixture 800 reduces the current that is suppliedto the low phosphor blue-shifted-yellow/green LED packages 840B toessentially zero. In some cases, it may be desirable or even necessaryto not allow the current to any of the LED packages to reach such lowlevels. In order to maintain minimum current levels (e.g., 50 mA) oneach string of LED packages, the locations of the color points for thethree (or more) different types of LED packages 840A, 840B, 850 may beset farther apart, as will be explained in greater detail with referenceto FIGS. 20A-20D.

In particular, FIG. 20A is an enlarged portion of the 1931 CIEChromaticity Diagram illustrating a range of color points that may beachieved using a modified version 800′ of the tunable troffer lightfixture 800 of FIG. 18A that has an extended tuning range. FIGS. 20B and20C are graphs comparing the lumen per watt and CRI performance of thetunable troffer light fixture 800 of FIG. 18A and the modified version800′ thereof that has the extended tuning range. FIG. 20D is a graphillustrating the change in current for various LED strings of thetunable troffer light fixtures 800, 800′ when driven to operate in eachof the five color point regions E3-E7 shown in FIG. 18C.

In order to fabricate the tunable troffer light fixture 800′, theblue-shifted-yellow/green LED packages 840A of light fixture 800 may bereplaced with blue-shifted-yellow/green LED packages 840A′ that haveincreased phosphor content, and the blue-shifted-yellow/green LEDpackages 840B of light fixture 800 may be replaced withblue-shifted-yellow/green LED packages 840B′ that have reduced phosphorcontent. For example, in the light fixture 800 of FIGS. 18A-18B, theblue-shifted-yellow/green LED packages 840A, 840B each used a LuAG:Cephosphor (and not other phosphors), with the LED packages 840A havingabout 3.6 times the amount of LuAG:Ce phosphor included in the LEDpackages 840B. In the light fixture 800′, this ratio was increased toabout 4.4. The blue-shifted-red LED packages 850 of light fixture 800were replaced with blue-shifted-red LED packages 850′ that includedabout 15% more red phosphor in light fixture 800′.

The effect of these changes may be seen in FIG. 20A. In particular, thepoints labeled 871, 872, 873 represent the color points for the threedifferent types of LED packages included in the light fixture 800. Byadjusting the relative currents provided to the three types of LEDpackages, the light fixture 800 may emit light having a color pointanywhere within the dashed-line triangle 890.

The points in FIG. 20A labeled 871′, 872′, 873′ represent the colorpoints for the three different types of LED packages 840A′, 840B′, 850′included in the modified light fixture 800′. By adjusting the relativecurrents provided to the three types of LED packages 840A′, 840B′, 850′,the modified light fixture 800′ may emit light having a color pointanywhere within the solid-line triangle 890′. As can be seen in FIG.20A, by further increasing the amount of phosphor included in the highphosphor blue-shifted-yellow/green LED packages 840A′ while decreasingthe amount of phosphor included in the low-phosphorblue-shifted-yellow/green LED packages 840B′, the light fixture 800′ isable to operate at a larger number of color points, and may operate inany of the E3-E7 color bins with non-zero drive currents for theblue-shifted-yellow/green LED packages 840A′, 840B′.

FIGS. 20B and 20C compare the projected lumens per watt and CRIperformance of the light fixtures 800 and 800′. As shown in thesefigures, the modified light fixture 800′ is projected to haveessentially equal or even better performance when operating in all fivecolor bins E3-E7.

FIG. 20D is a graph illustrating the change in current for various LEDstrings of the tunable troffer light fixtures 800, 800′ when the lightfixtures are driven to operate in each of the E3-E7 color bins. As shownin FIG. 20D, when the light fixtures 800 and 800′ are operated in theE5-E7 color bins (CCT values of 3000 K, 3500 K and 4000 K) the currentson each of the three strings are similar between the two devices.However, when operating in color bins E3 and E4 (CCT values of 4500 Kand 5000 K), the drive currents for the two strings ofblue-shifted-yellow/green LED packages 840A′, 840B′ in the modifiedlight fixture 800′ become closer together. Since under these conditionsmore LED packages are contributing to the light output, the lumens perwatt performance increases for the light fixture 800′ as compared to thelight fixture 800, which can be seen in the graph of FIG. 20B.

FIG. 21A is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating a range of color points that may be achieved using afurther modified version of the tunable troffer light fixture of FIG.18A that has a different extended tuning range. In FIG. 21A, the colorpoint for the blue-shifted-red LED packages is moved farther to theright to color point 871″, while the color points 872′, 873′ for the twoblue-shifted-yellow/green LED packages 840A′, 840B′ are unchanged.Consequently, a light fixture having the tuning range shown in FIG. 21Amay be formed using the LED packages 840A′, 840B′ discussed above alongwith blue-shifted-red LED packages 850″ that have a larger amount of redphosphor as compared to the blue-shifted-red LED packages 850′ discussedabove. As shown in FIG. 21A, the further modified version of the tunabletroffer light fixture of FIG. 18A may be used to emit light anywhere inthe triangle labeled 892. The triangle 892 is larger than the triangles890, 890′, and also covers all of the E3-E7 color bins with non-zerodrive currents for the blue-shifted-yellow/green LED packages 840A′,840B′.

FIG. 21B is an enlarged portion of the 1931 CIE Chromaticity Diagramillustrating how the light fixture 800 is tunable over a wider range ofcolor temperatures. As shown in FIG. 21B, by essentially turning off thelow phosphor blue-shifted-yellow/green LED packages 840B and increasingthe current to the high phosphor blue-shifted-yellow/green LED packages840A and to the blue-shifted-red LED packages 850, the light fixture 800may be tuned to emit light having a color temperature of 2200 K,although the color point of this light is offset from the black bodylocus. If the current to the low phosphor blue-shifted-yellow/green LEDpackages 840B is set at a low level (60 mA) the light fixture 800 maystill be tuned to emit light having a color temperature of 2200 K,although the color point of this light is even farther from the blackbody locus, as shown in FIG. 21B. Moreover, when theblue-shifted-yellow/green LED packages having higher phosphor loadingsare used, it is possible to generate light at 2200K that is on the blackbody locus.

The light fixtures according to the other embodiments of the presentinvention may similarly be tuned to such lower color temperatures, andthese light fixtures may also be tuned to higher color temperatures(e.g., 6500 K) while still remaining on or very near the black bodylocus.

FIG. 22A is a plan view of a light fixture 900 that is designed to betunable over the range shown by triangle 892 in FIG. 21. The lightfixture 900 includes a printed circuit board 930 having three differenttypes of LED packages mounted thereon. The LED packages comprise theabove-described high phosphor blue-shifted-yellow/green LED packages840A′, the low phosphor blue-shifted-yellow/green LED packages 840B′,and the blue-shifted-red LED packages 850″.

The light fixture 900 differs from the light fixtures 800 and 800′ inthat the light fixture 900 includes a larger number of blue-shifted-redLED packages 850′ and a smaller number of blue-shifted-yellow/green LEDpackages 840A′, 840B′. In particular, the light fixture 900 includesfifty high phosphor blue-shifted-yellow/green LED packages 840A′, fiftylow phosphor blue-shifted-yellow/green LED packages 840B′ and onehundred blue-shifted-red LED packages 850″. As a result, theblue-shifted-red LED packages 850″ in the middle row are spaced closelytogether while the blue-shifted-yellow/green LED packages 840A′, 840B′in each row on either side of the middle row are spaced farther apart.The use of more blue-shifted-red LED packages 850″ and lessblue-shifted-yellow/green LED packages 840A′, 840B′ increases theefficiency (and hence the lumens per watt performance) of the lightfixture 900 when operated at lower color temperatures.

Thus, pursuant to further embodiments of the present invention, thenumber of blue-shifted-red LED packages may be at least half the numberof blue-shifted-yellow/green LED packages. In other embodiments, thenumber of blue-shifted-red LED packages may be at least 75% the numberof blue-shifted-yellow/green LED packages. In still further embodiment,the number of blue-shifted-red LED packages may be at least equal to thenumber of blue-shifted-yellow/green LED packages.

FIG. 22B is a graph illustrating the intensity of the radiation emittedas a function of wavelength for the tunable troffer light fixture 900when operated to fall within each of the E3 through E7 regions or colorbins as compared to another tunable troffer light fixture that includessixty high phosphor blue-shifted-yellow/green LED packages, sixty lowphosphor blue-shifted-yellow/green LED packages and sixtyblue-shifted-red LED packages that are arranged in the manner shown inthe bottom portion of FIG. 18F. As can be seen in FIG. 22B, the use ofthe relatively higher number of blue-shifted-red LED packages 850″ inthe light fixture 900 results in a large reduction in the drive currentsupplied to the blue-shifted-red LED packages 850″, with almost nochange to the drive current supplied to the blue-shifted-yellow/greenLED packages 840A′, 840B′. This decrease in the drive current to theblue-shifted-red LED packages 850″ results in increased efficiency. Whenthe light fixture 900 is operated at low color temperatures (e.g., inthe E7 color bin), this may result in improved lumens per wattperformance of more than 3%.

FIG. 23 illustrates a modified printed circuit board design 930′ thatmay be used in the light fixture 900 in place of printed circuit board930. As shown in FIG. 23, the printed circuit boards 930, 930′ aresimilar, but in printed circuit board 930′ the blue-shifted-yellow/greenLED packages 840A′, 840B′ are staggered in the column direction. Sincethe LED packages are designed so that all of theblue-shifted-yellow/green LED packages 840A′, 840B′ are on duringoperation in all of color bins E3-E7, the printed circuit board 930′ mayexhibit improved color mixing as compared to the printed circuit board930.

FIG. 24 illustrates a printed circuit board design 1030 for a lightfixture according to further embodiments of the present invention. Theprinted circuit board 1030 may be used, for example, in the lightfixture 900 in place of printed circuit board 930. The light fixture maybe, for example, a 2′×2′ troffer light fixture. The printed circuitboard 1030 may provide even further improved color mixing through thearrangement of the LED packages.

As shown in FIG. 24, the printed circuit board 930 includes fiftyblue-shifted-yellow/green LED packages 840A′, fiftyblue-shifted-yellow/green LED packages 840B′ and one hundredblue-shifted-red LED packages 850″ that are arranged in three rows 1060,1062, 1064. The blue-shifted-yellow/green LED packages 840A′, 850B′ arearranged in strings of ten LEDs each so that there are five strings ofblue-shifted-yellow/green LED packages 840A′, five strings ofblue-shifted-yellow/green LED packages 840B′ and ten strings ofblue-shifted-red LED packages 850″. The blue-shifted-yellow/green LEDpackages 840A′ and the blue-shifted-yellow/green LED packages 840B′ arearranged in a criss-cross pattern like the pattern shown in the bottomportion of FIG. 18F. The blue-shifted-yellow/green LED packages 840A′,840B′ are in the outside rows 1062, 1064 while the blue-shifted-red LEDpackages 850″ are in the interior row 1060.

In the embodiment of FIG. 24, the spacing between theblue-shifted-yellow/green LED packages 840A′, 840B′ in the two rows1062, 1064 of blue-shifted-yellow/green LED packages 840A′, 840B′ is notuniform. In particular, the distance between adjacentblue-shifted-yellow/green LED packages 840A′, 840B′ changes in the lastten blue-shifted-yellow/green LED packages 840A′, 840B′ in each row1062, 1064. In particular, the six strings of blue-shifted-yellow/greenLED packages 840A′, 840B′ that form the middle portions of rows 1062,1064 may have space the blue-shifted-yellow/green LED packages 840A′,840B′ a uniform distance apart while the four strings ofblue-shifted-yellow/green LED packages 840A′, 840B′ that are one theends of the two rows 1062, 1064 may have space theblue-shifted-yellow/green LED packages 840A′, 840B′ may space the LEDpackages apart in a non-uniform manner. This arrangement may allow thethree LED packages 840A′, 840B′, 850″ that are the last LED packages oneach of the three rows 1060, 1062, 1064 to be aligned in the columndirection, as shown in the enlarged call-out of FIG. 24.

The LED package layout of FIG. 24 may be advantageous because when alight fixture that includes the printed circuit board 1030 is operatedat or near either end of its tunable range (e.g., at a color temperatureof about 3000 K or a color temperature of about 5000 K for an embodimentthat is tunable over the E3-E7 color bins) one of theblue-shifted-yellow/green LED packages 840A′ or theblue-shifted-yellow/green LED packages 840B′ will be driven by arelatively high current while the other of the blue-shifted-yellow/greenLED packages 840A′ or the blue-shifted-yellow/green LED packages 840B′will be driven at a very low current. By aligning the three LED packages840A′, 840B′, 850″ that are on each end of the three rows 1060, 1062,1064 in the column direction, the mixing of the emitted light may beenhanced. In particular, the arrangement of the LED packages 840A′,840B′, 850″ on the printed circuit board 1030 may reduce or eliminatethe appearance of a red splotch of light and/or a yellow or greensplotch of light that may otherwise appear at the end of the printedcircuit board 1030 when a light fixture including the printed circuitboard 1030 is operated near either end of its tunable color temperaturerange.

Thus, in some embodiments of the present invention, the LED packages ina row of LED packages may not be uniformly spaced. In some cases, theLED packages in a middle portion of a row may have a uniform spacingwhile the LED packages at either end of the row may have a non-uniformspacing. In some embodiments, the LED packages in a central row ofblue-shifted-red LED packages may have a uniform spacing while the LEDpackages in one or more outer rows of blue-shifted-yellow/green LEDpackages may have non-uniform spacing, at least in the outer portions ofeach row of blue-shifted-yellow/green LED packages.

It will also be appreciated that tunable light fixtures may be providedusing the techniques disclosed herein that are tunable over a broaderrange of color points and color temperatures. For example, according tofurther embodiments of the present invention, light fixtures may beprovided that are tunable to color temperatures as low as 2200 K and/orto as high as 10000 K. When tuning to low color temperatures such ascolor temperatures of 2200-2500 K, the color point of the combined lightoutput will generally be below the black body locus on the 1931 CIEChromaticity Diagram. In order to achieve these low color temperatures,a larger percentage of the LED packages may be blue-shifted-red LEDpackages. Additionally, the amount of phosphor included in at least someof the blue-shifted-red LED packages may be increased to facilitateachieving these lower color temperatures. The higher color temperaturesmay be achieved, for example, by further reducing the amount of phosphorincluded in at least some of the low phosphor blue-shifted-yellow/greenLED packages.

It will also be appreciated that in other embodiments additional LEDpackages may be used to achieve tunability over a larger range of colortemperatures. For example, FIG. 19C schematically depicts a lightfixture that uses three different types of blue-shifted-yellow/green LEDpackages. In FIG. 19C, the middle row 860 may comprise blue-shifted-redLED packages 850, the rows 862, 864 on either side of the middle row 850may each include both low phosphor and high phosphorblue-shifted-yellow/green LED packages 840A, 840B (which use a LuAG:Cephosphor), and the outside rows 866, 868 may each include high phosphorblue-shifted-yellow/green LED package 842 that includes a YAG:Cephosphor. The blue-shifted-yellow/green LED packages 842 may have acolor point that is to the right of the color point for the highphosphor blue-shifted-yellow/green LED packages 840A on the 1931 CIEChromaticity Diagram. The blue-shifted-yellow/green LED packages 842 mayfacilitate emitting light at lower color temperatures with improvedefficiency. In other embodiments, the blue-shifted-yellow/green LEDpackages 842 could be included as part of the middle row 860.

In some embodiments, the light fixtures disclosed herein may be used inconjunction with dimming circuits. Typically, pulse width modulation(PWM) dimming circuits are used to dim white light emitting solid statelight fixtures. With PWM dimming, the current is delivered to the LEDpackages using a duty cycle approach where the current is fed to the LEDpackages as a square wave where the current is provided during oneportion of the waveform and not provided during the other. The LEDpackages thus turn on and off at the frequency of the square wave. Atypical frequency for the square wave is 75 Hz, which is high enoughthat the human eye cannot determine that the LED packages are turning onand off. The amount of dimming may then be readily controlled byadjusting the duty cycle of the square wave (i.e., the percentage oftime during a period of the square wave that the LED package is turnedon).

PWM dimming may be advantageous because it does not requiring changingthe amount of current provided to the LED packages; instead, currenteither is or is not supplied to the LED packages using the square wavedrive current. When a linear dimming is used instead of a PWM approachthe light fixture is dimmed by reducing the currents supplied to the LEDpackages. The potential problem with linear dimming is that differenttypes of LEDs may perform differently as the current is reduced, both interms of the relative amount of light emitted and also in terms of thepeak wavelength of the emitted light. These factors may also bedependent on the operating temperature of the LEDs. Moreover, as theLEDs in the LED packages age, these factors may change, and they maychange at different rates and in different ways for different types ofLEDs. Thus, it may be difficult and/or expensive to design a controlsystem that can ensure consistent dimming when linear dimming is used.

As discussed above, in some embodiments of the present invention, thesame (or very similar) LEDs may be used to fabricate both theblue-shifted-yellow/green LED packages and the blue-shifted-red LEDpackages. As such, the LEDs will change in the same manner during lineardimming in terms of the amount of light emitted and the peak wavelengthof the light. Moreover, gallium nitride based blue LEDs tend to exhibitmuch smaller changes with both current and temperature than do red LEDssuch as AlInGaP LEDs. Because of these differences, linear dimming maybe used in the light fixtures according to embodiments of the presentinvention. This has the potential for simplifying the control circuit.Moreover, in some applications low frequency PWM dimming may beunacceptable, and the use of linear dimming provides a work around inthese applications.

Various embodiments of the invention that are described above providemechanisms for improving color mixing by the arrangement of the LEDpackages. These arrangements have primarily been described with respectto troffer light fixtures that have long rows of LED packages. However,it will be appreciated that these same techniques may be used withrespect to other LED arrangements and other types of solid state lightfixtures. Several examples of other types of embodiments will now bedescribed with reference to FIGS. 25A-25B.

For example, FIG. 25A is a schematic plan view of a printed circuitboard (or other submount) 1100 that includes a first, second and thirdtypes of wavelength-converted LED packages 1102, 1104, 1106. The LEDpackages 1102, 1104, 1106 are arranged in three circular patterns 1110,1112, 1114 on the printed circuit board 1100. The LED packages 1102 maycomprise, for example, a first type of blue-shifted-yellow/green LEDpackages, the LED packages 1104 may comprise, for example, a second typeof blue-shifted-yellow/green LED packages, and the LED packages 1106 maycomprise, for example, blue-shifted-red LED packages. The LED packages1102 and 1104 may be in the outer circular pattern 1114 and the innercircular pattern 1112, while the LED packages 1106 may be in theintermediate circular pattern 1110 that is between the inner and outercircular patterns 1112, 1114. This may provide improved color mixing.Additionally, the LED packages 1106 in the intermediate circular pattern1110 may be arranged between the LED packages 1102, 1104 in the outercircular pattern 1112, and the LED packages 1102, 1104 in the innercircular pattern 1112 may be arranged between the LED packages 1106 inthe intermediate circular pattern 1110. Each different type of LEDpackage 1102, 1104, 1106 may be in its own LED string (or set of LEDstrings). The arrangement shown in FIG. 25A generally surrounds the LEDpackages 1106 with LED packages 1102 and 1104 to reduce or prevent theLED packages 1106 from being individually visible to a human observer.The arrangement also intersperses the LED packages 1102, 1104 so thateach LED package 1106 will always have at least one LED package 1102 or1104 near it that is driven with a relatively high current regardless ofthe color temperature to which the light fixture is tuned.

FIG. 25B is a schematic plan view of a printed circuit board (or othersubmount) 1120 according to further embodiments of the presentinvention. First, second and third types of wavelength-converted LEDpackages 1122, 1124, 1126 are mounted on the printed circuit board 1120.The LED packages 1122 may comprise, for example, a first type ofblue-shifted-yellow/green LED packages, the LED packages 1124 maycomprise, for example, a second type of blue-shifted-yellow/green LEDpackages, and the LED packages 1126 may comprise, for example,blue-shifted-red LED packages. The LED packages 1122, 1124, 1126 arearranged so that the blue-shifted-red LED packages 1126 are surroundedby the blue-shifted-yellow/green LED packages 1122, 1124. This again mayprovide improved color mixing.

In FIGS. 25A-25B, the LED packages 1102, 1104, 1106, 1122, 1124, 1126may be any of the LED packages according to embodiments of the presentinvention disclosed herein. The design of FIG. 25A may be suitable foruse in A-series bulbs and downlights.

Any of the embodiments disclosed herein may include a power circuithaving a buck regulator, a boost regulator, a buck-boost regulator, afly-back converter, a SEPIC power supply, or the like and/or a multiplestage power converter employing the like, and may comprise a drivercircuit as disclosed in U.S. patent application Ser. No. 14/291,829,filed May 30, 2014, entitled “High Efficiency Driver Circuit with FastResponse” by Hu et al. or U.S. patent application Ser. No. 14/292,001,filed May 30, 2014, entitled “SEPIC Driver Circuit with Low InputCurrent Ripple” by Hu et al. incorporated by reference herein. Thecircuit may further be used with light control circuitry that controlscolor temperature of any of the embodiments disclosed herein, such asdisclosed in U.S. patent application Ser. No. 14/292,286, filed May 30,2014, entitled “Lighting Fixture Providing Variable CCT” by Pope et al.incorporated by reference herein. Additionally, any of the embodimentsdescribed herein can include driver circuitry disclosed in U.S. patentapplication Ser. No. 15/018,375, titled Solid State Light FixturesHaving Ultra-Low Dimming Capabilities and Related Driver Circuits andMethods, filed on Feb. 8, 2016 and assigned to the same assignee as thepresent application, the entirety of this application being incorporatedherein by reference.

For example, the LED emitters can be arranged in series, parallel orseries-parallel configurations and the voltage that passes through thedifferent color emitters can be adjusted via control circuitry to adjustthe color emitted by the lighting device. Such voltage adjustment may beused, for example, to change the ratio of current passing throughdifferent color LED emitters to achieve the above-described dimming to awarmer correlated color temperature light. This can be done in a seriesconfiguration by controlling an amount of current that is shunted aroundLED emitters of certain color and/or color temperature. In otherembodiments, the LEDs may be arranged in strings of LED emitters of thesame color and/or color temperature (e.g., a string of blue-shiftedyellow/green LED packages and a string of blue-shifted-red LED packages)and these strings can be independently controlled to obtain the desiredlight color and/or color temperature or color/intensity combination.Other arrangements are possible.

Further, any of the embodiments disclosed herein may be used in aluminaire having one or more communication components forming a part ofthe light control circuitry, such as an RF antenna that senses RFenergy. The communication components may be included, for example, toallow the luminaire to communicate with other luminaires and/or with anexternal wireless controller, such as disclosed in U.S. Pat. No.8,975,827, filed Mar. 1, 2013, entitled “Lighting Fixture forDistributed Control” or U.S. Provisional Application No. 61/932,058,filed Jan. 27, 2014, entitled “Enhanced Network Lighting” both owned bythe assignee of the present application and the disclosures of which areincorporated by reference herein. More generally, the control circuitrycan include at least one of a network component, an RF component, acontrol component, and one or more sensors. A sensor, such as aknob-shaped sensor, may provide an indication of ambient lighting levelsand/or occupancy within the room or illuminated area. Other sensors arepossible, and a sensor may be separate from and/or integrated into thelight control circuitry. Depending on the embodiment, the light can haveintegrated logic that locally controls the light based on the sensorinput, and/or the light can pass the sensor data to a central controlthat controls the light, e.g., from a central computer that is linked tothe lights via a communication network.

The LED packages discussed herein may be mounted directly on a printedcircuit board (e.g., chip on board) and/or packaged phosphor-convertedwhite or color LED packages mounted on the printed circuit board, suchas a metal core printed circuit board or FR4 board. In some embodiments,the LED packages can be mounted directly to the heat sink or anothertype of board or substrate. Depending on the embodiment, the lightingdevice can employ LED package arrangements or lighting arrangementsusing remote phosphor technology as would be understood by one ofordinary skill in the art, and examples of remote phosphor technologyare described in U.S. Pat. No. 7,614,759, assigned to the assignee ofthe present invention and hereby incorporated by reference.

The LED packages may be disposed in different configurations and/orlayouts as desired, for example utilizing single or multiple strings ofLED packages where each string of LED packages comprise LED packages inseries and/or parallel. Different color temperatures and appearancescould be produced using other LED and/or LED package combinations. Ifdesirable, other arrangements are possible. In some embodiments, astring, a group of LED packages or can comprise different lightingcharacteristics and by independently controlling a string, a group ofLED packages or individual LED packages, characteristics of the overalllight out output of the device can be controlled.

In some embodiments, each LED packages may comprise one or more LEDsdisposed within a coupling cavity with an air gap being disposed betweenthe LED and a light input surface. In any of the embodiments disclosedherein each of the LED element(s) or module(s) can have different or thesame light distribution, although each may have a directional emissiondistribution (e.g., a side emitting distribution), as necessary ordesirable. More generally, any lambertian, symmetric, wide angle,preferential-sided or asymmetric beam pattern LED element(s) ormodule(s) may be used as the light source.

Moreover, depending on the embodiment, the desired light distributioncan be achieved by single primary optics of packaged LEDs and/orcombinations of the primary optics of packaged LEDs with single ormultiple secondary optics. Optical components can be the same or varyfrom LED element to LED element depending on the desired lightingcharacteristics of the luminaire. In some embodiments, LED optics canemploy waveguide technology where internal reflection of light isutilized along with light extraction features to achieve a desired lightdistribution.

In various embodiments described herein various smart technologies maybe incorporated in the light fixtures as described in the followingapplications “Solid State Lighting Switches and Fixtures ProvidingSelectively Linked Dimming and Color Control and Methods of Operating,”application Ser. No. 13/295,609, filed Nov. 14, 2011, which isincorporated by reference herein in its entirety; “Master/SlaveArrangement for Lighting Fixture Modules,” application Ser. No.13/782,096, filed Mar. 1, 2013, which is incorporated by referenceherein in its entirety; “Lighting Fixture for Automated Grouping,”application Ser. No. 13/782,022, filed Mar. 1, 2013, which isincorporated by reference herein in its entirety; “Multi-AgentIntelligent Lighting System,” application Ser. No. 13/782,040, filedMar. 1, 2013, which is incorporated by reference herein in its entirety;“Routing Table Improvements for Wireless Lighting Networks,” applicationSer. No. 13/782,053, filed Mar. 1, 2013, which is incorporated byreference herein in its entirety; “Commissioning Device for Multi-NodeSensor and Control Networks,” application Ser. No. 13/782,068, filedMar. 1, 2013, which is incorporated by reference herein in its entirety;“Wireless Network Initialization for Lighting Systems,” application Ser.No. 13/782,078, filed Mar. 1, 2013, which is incorporated by referenceherein in its entirety; “Commissioning for a Lighting Network,”application Ser. No. 13/782,131, filed Mar. 1, 2013, which isincorporated by reference herein in its entirety; “Ambient LightMonitoring in a Lighting Fixture,” application Ser. No. 13/838,398,filed Mar. 15, 2013, which is incorporated by reference herein in itsentirety; “System, Devices and Methods for Controlling One or MoreLights,” application Ser. No. 14/052,336, filed Oct. 10, 2013, which isincorporated by reference herein in its entirety; and “Enhanced NetworkLighting,” application No. 61/932,058, filed Jan. 27, 2014, which isincorporated by reference herein in its entirety.

Additionally, any of the luminaire embodiments described herein caninclude the smart lighting control technologies disclosed in U.S.Provisional Application Ser. No. 62/292,528, titled Distributed LightingNetwork, filed on Feb. 8, 2016 and assigned to the same assignee as thepresent application, the entirety of this application being incorporatedherein by reference.

While embodiments of the present invention have primarily been discussedabove with respect to troffer and A-series light fixtures, it will beappreciated that the techniques disclosed herein are applicable to awide range of other types of light fixtures. For example, U.S. PatentPublication No. 2014/0347885 discloses light fixtures that have opticalwaveguide bodies. It will be appreciated that the techniques disclosedherein may also be used in these optical waveguide luminaires.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

The present invention has been described above with reference to theaccompanying drawings, in which certain embodiments of the invention areshown. However, this invention should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the thickness of layers and regions are exaggerated forclarity. Like numbers refer to like elements throughout. As used hereinthe term “and/or” includes any and all combinations of one or more ofthe associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that, when used in thisspecification, the terms “comprises” and/or “including” and derivativesthereof, specify the presence of stated features, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, operations, elements, components, and/or groupsthereof.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions and/orlayers, these elements, components, regions and/or layers should not belimited by these terms. These terms are only used to distinguish oneelement, component, region or layer from another element, component,region or layer. Thus, a first element, component, region or layerdiscussed below could be termed a second element, component, region orlayer without departing from the teachings of the present invention.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1-52. (canceled)
 53. A light emitting diode (LED) based light fixture,comprising: a plurality of blue-shifted-yellow/green LED packages, theblue-shifted-yellow/green LED packages including low-phosphor LEDpackages and high phosphor LED packages, the high phosphor LED packageshaving a higher phosphor conversion ratio than the low phosphor LEDpackages; and a plurality of blue-shifted-red LED packages, wherein theblue-shifted-red LED packages extend in a first row, and wherein a firstsubset of the blue-shifted-yellow/green LED packages extend in a secondrow on a first side of the blue-shifted-red LED packages and a secondsubset of the blue-shifted-yellow/green LED packages extend in a thirdrow on a second side of the blue-shifted-red LED packages that isopposite the first side.
 54. The LED based light fixture of claim 53,wherein the blue-shifted-yellow/green LED packages in the second rowinclude both low phosphor LED packages and high phosphor LED packages.55. (canceled)
 56. The LED based light fixture of claim 54, wherein theblue-shifted-red LED packages are electrically connected in series toform a first LED string and the low phosphor LED packages areelectrically connected in series to form a second LED string, whereinthe second LED string crosses the first LED string in at least fourlocations.
 57. The LED based light fixture of claim 56, wherein the highphosphor LED packages are electrically connected in series to form athird LED string, and wherein the third LED string crosses the first LEDstring in at least four locations.
 58. (canceled)
 59. The LED basedlight fixture of claim 53, wherein a first end of the second row extendsbeyond a first end of the first row, and a second end of the second rowextends beyond a second end of the first row.
 60. (canceled)
 61. The LEDbased light fixture of claim 53, wherein the high phosphor LED packageseach include a first amount of a first phosphor and the low phosphor LEDpackages each include a second amount of the first phosphor, wherein thefirst amount is between twice and seven times the second amount. 62.(canceled)
 63. The LED based light fixture of claim 53, wherein anaverage separation between adjacent ones of the blue-shifted-red LEDpackages in the first row is less than an average separation betweenadjacent ones of the blue-shifted-yellow/green LED packages in thesecond row.
 64. (canceled)
 65. The LED based light fixture of claim 53,wherein all of the LED packages in the second row are not spaced apartfrom adjacent LED packages in the second row by a uniform amount, andwherein all of the LED packages in the third row are not spaced apartfrom adjacent LED packages in the second row by a uniform amount. 66-69.(canceled)
 70. A tunable light emitting diode (LED) based light fixture,comprising: a plurality of blue-shifted-yellow/green LED packages, theblue-shifted-yellow/green LED packages including low-phosphor LEDpackages that each include a first amount of a first phosphor and highphosphor LED packages that each include a second amount of the firstphosphor; and a plurality of blue-shifted-red LED packages; wherein thesecond amount is between twice and seven times the first amount.
 71. Thetunable LED based light fixture of claim 70, wherein theblue-shifted-red LED packages extend in a first row and theblue-shifted-yellow/green LED packages extend in a second row and in athird row, with the second row extending on a first side of the firstrow and the third row extending on a second side of the first row thatis opposite the first side.
 72. (canceled)
 73. The tunable LED basedlight fixture of claim 71, wherein the second row includes both lowphosphor LED packages and high phosphor LED packages, and wherein thethird row includes both low phosphor LED packages and high phosphor LEDpackages.
 74. The tunable LED based light fixture of claim 70, whereinthe blue-shifted-red LED packages are electrically connected in seriesto form a first LED string and the low phosphor LED packages areelectrically connected in series to form a second LED string, andwherein the second LED string crosses the first LED string in at leastfour locations. 75-76. (canceled)
 77. The tunable LED based lightfixture of claim 71, wherein a second line defined by the second row hasrespective endpoints that extend beyond respective endpoints of a firstline defined by the first row.
 78. (canceled)
 79. The tunable LED basedlight fixture of claim 71, wherein an average separation betweenadjacent ones of the blue-shifted-red LED packages in the first row isless than an average separation between adjacent ones of theblue-shifted-yellow/green LED packages in the second row.
 80. (canceled)81. The LED based light fixture of claim 70, wherein a total number ofblue-shifted-red LED packages included in the LED based light fixture isgreater than 0.75 times a total number of blue-shifted-yellow/green LEDpackages included in the LED based light fixture. 82-86. (canceled) 87.A light emitting diode (LED) based light fixture, comprising: aplurality of blue-shifted-yellow/green LED packages, theblue-shifted-yellow/green LED packages including low-phosphor LEDpackages and high phosphor LED packages, the high phosphor LED packageshaving a higher phosphor conversion ratio than the low phosphor LEDpackages; and a plurality of blue-shifted-red LED packages, wherein theblue-shifted-yellow/green LED packages surround the blue-shifted-red LEDpackages.
 88. The LED based light fixture of claim 87, wherein at leastsome of the blue-shifted-yellow/green LED packages are arranged in afirst circle and the blue-shifted-red LED packages are arranged in asecond circle that is within the first circle.
 89. The LED based lightfixture of claim 88, wherein additional of the blue-shifted-yellow/greenLED packages are arranged in a third first circle that is within thesecond circle.
 90. The LED based light fixture of claim 87, wherein theblue-shifted-yellow/green LED packages in the first circle include bothlow phosphor LED packages and high phosphor LED packages that arearranged in alternating order. 91-92. (canceled)
 93. The LED based lightfixture of claim 87, wherein the high phosphor LED packages each includea first amount of a first phosphor and the low phosphor LED packageseach include a second amount of the first phosphor, wherein the firstamount is between twice and seven times the second amount. 94.(canceled)